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Vol. 8. Issue 5.
Pages 3978-3987 (September - October 2019)
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Vol. 8. Issue 5.
Pages 3978-3987 (September - October 2019)
Original Article
DOI: 10.1016/j.jmrt.2019.07.006
Open Access
Mott insulator behavior in the yttrium-based antimoniate oxide Ba2YSbO6
J.A. Grisales Ceróna, J. Arbey Rodríguezb, A. Rosales-Riverac, N.A. Salazar H.c, J.A. Cuervo Farfána, J.A. Cardona Vasqueza, D.A. Landínez Télleza,b, J. Roa-Rojasa,
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Corresponding author.
a Grupo de Física de Nuevos Materiales, Departamento de Física, Universidad Nacional de Colombia, Bogotá, DC, Colombia
b Grupo de Estudios de Materiales - GEMA, Departamento de Física, Universidad Nacional de Colombia, Bogotá, DC, Colombia
c Laboratorio de Magnetismo y Materiales Avanzados, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Colombia Sede Manizales, Manizales, Colombia
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Tables (2)
Table 1. Wyckoff positions and tolerance factor obtained from the Rietveld refinement for the Ba2YSbO6 perovskite compound.
Table 2. Experimental and expected weight percentage for the Ba2YSbO6 material obtained from the deconvolution of the EDX spectrum.
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A careful experimental and theoretical study of the double perovskite type material Ba2YSbO6 is reported. The results show that this yttrium-based antimoniate oxide crystallizes in a cubic structure, Fm3¯m (#225) space group, with evidence of the cationic ordering that characterizes a rocksalt superstructure, and tolerance factor slightly less than the unit (τ = 0.9791) due to the size differences between the Y-O6 and Sb-O6 octahedrons. The magnetic response shows weak ferromagnetic effects for the temperature values studied (50, 200 and 300 K), with evidence of an antiferromagnetic reentrance at T = 118 K under the application of low magnetic fields, which is attributed to the presence of polar ordering, accompanied by octahedral distortions caused by the movement of the cations Y3+ and Sb5+, whose effects are no longer observed in the presence of a fairly high external magnetic field (of the Tesla order). The results of the optical characterization by diffuse reflectance suggest the occurrence of a band gap Eg = 4.61 eV, which is characteristic of an insulating material. The electronic structure calculations corroborate the insulating nature of the Ba2YSBO6 complex perovskite. The results allow classifying this material as a Mott insulator, in which the occurrence of intra-site spin-exchange facilitates unpaired spins to the 4d-t2g Yttrium states, mediated by the 2p Oxygen orbitals and 5p Antimony orbitals, resulting in the ferromagnetic character of the insulating material.

Antimoniate yttrium-based perovskite
Structural characterization
Magnetic response
Optical band gap
Electronic structure
Full Text

Due to the possibility of modifying its chemical composition, the double perovskite type materials with generic formula A2BB′O6 exhibit extremely interesting and apparently unusual physical properties, which have been the subject of extensive study during the last decades [1]. Currently, particular efforts are devoted to the search of the basic physical mechanisms that favor the properties that the perovskites show, by developing theoretical models that replicate them and characterizing new materials, using experimental techniques that are increasingly sophisticated and precise [2]. On the other hand, materials engineering is concerned with the applications of this unique family in the innovation of devices, constituting an area of research open to many revolutionary discoveries ranging from superconducting materials [3] to magnetic semiconductors [4], multiferroic materials [5], colossal magnetoresistive [6] and magnetocalorics [7], among others. The potential applicability of perovskites are so varied that they include uses in sensors and catalytic electrodes, certain types of fuel cells, solar cells, lasers, devices for storing and processing information in magnetic and magneto-electric media, as well as applications in the recent spintronics industry [8]. Usually site A of the A2BB′O6 perovskite is occupied by an alkaline earth element and sites B and B' by transition metals or rare earths. Although when B and B′ are constituted by transition metals with sufficiently small ion radii, site A can be occupied by a rare earth. Within this family of complex ceramics, synthesis of a subfamily of antimonite oxides based on rare earths with Ba in site A was reported in the 1980s. The general formula was established as Ba2LnSbO6 (Ln=Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb) and only preliminary structural and magnetic characterizations were carried out [9]. Because at that time tools such as Rietveld refinement were lacking, which currently allows more detailed analysis of experimental X-ray diffraction data, it was reported that for all Ln the materials crystallize with a cubic structure, belonging to the spatial group Fm3¯m. It is necessary to recognize that, considering the instrumental limitations of the time, these results do not differ much from recent reports, except in the case of Ln = Nd, for which it has been reported that the structure is rhombohedral, belonging to the R3¯ space group, with a cell parameter 2.5 Å lower than that reported 30 years ago [10]. Other studies of diverse physical properties have been carried out in this perovskite-type antimoniates based on rare earths, with results that demonstrate their insulating and paramagnetic characteristics [11–13]. When substituting trivalent rare earth by another cation of lower ionic radius, also trivalent, such as Yttrium (Ba2YSbO6) by using the solid-state reaction technique, the unit cell remained cubic and its volume remained within the average value reported for Ba2LnSbO6 materials [14]. Subsequent reports of this material, following different synthesis routes such as hydrothermal [15] and combustion [16] confirmed this result. Recently, an ab-initio study on the density of the states and the band structure was published, which briefly analyzes only the result relative to the energy value of the gap compared with an experimental result obtained from a spectrum of diffuse reflectance [17]. Because the perovskite Ba2YSbO6 has not been sufficiently studied, the aim of this work is to report an exhaustive characterization of the crystalline structure of this solid reacted material, besides analyzing the surface morphology, the composition, the electrical transport characteristic, the magnetic susceptibility and optical response, in addition to a detailed study of the electronic structure, including the contributions to the density of states in the vicinity of the Fermi level, due to the 4d1 orbitals of the Y3+ and 5p3 of the Sb5+, as well as the mechanisms that give rise to the electrical, magnetic and optical responses of this interesting material.

2Experimental setup

The samples were produced by applying the standard solid state reaction technique, from the precursor oxides of BaCO3, Y2O3 and Sb2O5 (Aldrich 99.99%), which were dried at 200 °C and weighed in stoichiometric proportions, according to the composition given by the formula Ba2YSbO6. Subsequently, the powdered oxides were mixed and crushed in an agate mortar for a period of 3 h until a homogeneous mixture of uniform granular appearance was obtained. The stoichiometric powder samples were calcined at a temperature of 1000 °C for a time of 24 h, after which they were milled for 0.5 h, pressed into tablets of 7.0 ± 0.1 mm in diameter and 2.5 ± 0.1 mm thick, and subjected to a thermal sintering process at 1200 °C for 24 h. The structural characterization of the material was carried out by means of X-ray diffraction experiments (XRD), using a Panalytical X-Pert PRO MPD diffractometer with wavelength radiation λCuKα = 1.540598 Å, with subsequent Rietveld refinement of the experimental data, for which the GSAS code was used [18]. The surface morphological study of the samples was carried out through scanning electron microscopy (SEM) images using a VEGA 3 Tescan microscope. A compositional analysis of the material took place by means of a microprobe for studies of energy dispersion spectroscopy by electrons (EDX), which was performed by using a Bruker X-ray gun coupled to the electron microscope. The magnetic response was established through measurements of magnetic susceptibility as a function of temperature (in the regime between 50 and 300 K), following the procedures ZFC and FC, under the application of magnetic field strengths of 0.2, 0.5, 2.0, 10, 20 and 30 kOe, as well as isothermal curves of magnetization hysteresis as a function of the applied field, for which a PPMS VersaLab Design equipment was used. The energy gap was measured by Kubelka-Munk type adjustments of diffuse reflectance spectra, measured on a VARIAN Cary 5000 UV–vis-NIR spectrophotometer, which has an integration sphere with a PMT/Pbs detector. Finally, measurements of electrical resistivity as a function of temperature were made in a DC resistometer, in the range between 77 and 300 K and the dielectric constant was established by means of an Agilent HP4194A-350 frequency analyzer in the frequency regime from 100 Hz to 40 MHz.

3Calculation method

The theoretical study of the structural and electronic properties of the double perovskite Ba2YSbO6 was carried out through the implementation of the Wien2k [19] program, which is based on the density functional theory (DFT) [20,21] that has proved to be a practical and effective tool in the prediction of these properties in novel materials [22–24]. The Wien2k was chosen for the calculations due to the full-potential augmented plane-wave (LAPW) + local orbital (lo) method that it uses, guaranteeing a good precision in the band structure calculations. Likewise, it was considered an exchange and correlation potential through the use of the generalized gradient approximation (GGA) [25], which allows taking into account the polarization of the electronic turns for the study of the magnetic character of the material. The crystallographic lattice parameter was theoretically obtained through the minimization of energy with respect to the volume of the unit cell. The calculations were carried out considering a cubic perovskite structure, Fm3¯m (#225) space group, with muffin-tin radii BaRMT = 2.50 Å, YRMT = 2.02 Å, SbRMT = 1.95 Å and ORMT = 1.65 Å. The base plane wave size was determined by an RMT*Kmax = 7.50, which is equivalent to a flat wave cutoff energy of 281.11 eV = 20.66 Ry. 2500 k-points over the irreducible Brillouin zone were used, with a maximum angular momentum inside the muffin-tin sphere of l = 10.

4Results and discussion4.1Structural characterization

The experimental XRD pattern, corresponding to the double perovskite Ba2YSbO6 monophasic between 10 and 90 degrees in 2θ, measured in a scan time of 2 s with step of 0.01°, is shown in Fig. 1. The diffractogram consists of peaks with high intensities, which are characteristic of a primitive cubic perovskite, plus some reflections with weak lines that characterize the superstructure, i.e., Y and Sb cations adopt an ordered and alternating arrangement along the crystallographic axes (cationic ordering), in the same way as in the NaCl structure. In order to accurately establish the properties and structural parameters of the material, a detailed Rietveld refinement procedure was carried out on the experimental data by using the GSAS code with EXPGUI interface [26]. The quality of the refinement can be corroborated through the values of the main parameters of the refinement: χ2 = 3.112, RF = 2.38%, Rwp = 4.17% and RP = 3.03%, which is clear in Fig. 1, where a good correspondence between simulated and experimental diffraction patterns can be observed. The results reveal that the Ba2YSbO6 material crystallizes in a cubic double perovskite structure, Fm3¯m (# 225) space group, as expected for most family compounds Ba2LnSbO6[27]. The cell parameter obtained through the refinement process was a = 8.4182(0) Å. This spatial group suggests that the cation Ba2+ with the highest ionic radius (1.56 Å) occupies the position A of the perovskite A2BB'O6 and the cations Y3+ (ionic radius 0.95 Å) and Sb5+ (ionic radius 0.62 Å) occupy the B sites and B′. The presence of the insipient reflection lines (111), (311), (331), (333) and (511) in the diffractogram, constitute the fingerprint of formation of an ordered cubic perovskite structure, also called superstructure. Then, in the double cubic perovskite Ba2YSbO6 there exist cationic ordering, i.e., the cations Y3+ and Sb5+ are arranged alternately along the crystallographic axes of the structure, forming a perfect rock salt. Table 1 reports the most relevant crystallographic parameters obtained through the refinement of the XRD experimental data.

Fig. 1.

XRD refined pattern for the Ba2YSbO6 double perovskite. Black symbols represent the experimental diffraction data, continuous line is the calculated pattern and the difference between the experimental and calculated patterns is represented by the base line.

Table 1.

Wyckoff positions and tolerance factor obtained from the Rietveld refinement for the Ba2YSbO6 perovskite compound.

Atomic coordinates - Fm3¯m space group - τ = 0.9791
Atom  Wyckoff position  x  y  z 
Ba2+(1)  8c  0.2500  0.2500  0.7500 
Ba2+(2)  8c  0.7500  0.7500  0.2500 
Y3+  4a  0.0000  0.0000  0.0000 
Sb5+  4b  0.5000  0.5000  0.5000 
O2(1)  24e  0.0000  0.7378  0.0000 
O2(2)  24e  0.2622  0.0000  0.0000 

In the analysis of crystalline structures the concept of position is fundamental [28]. For this reason, in Table 1 the positions of Wyckoff are presented for the cubic double structure of the Ba2YSbO6. In the Wyckoff notation, a, b, c and e are the Wyckoff letters that determine all the points for which the site-symmetry groups are conjugate subgroups of the Fm3¯m [29]. The number of equivalent points per unit cell, which accompanies the letter of Wyckoff, is known as multiplicity of the Wyckoff position. In Table 1, τ represents the Goldschmidt tolerance factor [30], which has been extensively used to predict the stability of the perovskite structure based only on the chemical formula and the ionic radii of each ion present in the structure [31]. The value obtained for the tolerance factor (τ = 0.9791) differs 2.1% from the expected value for a cubic perovskite structure, which suggests the existence of some kind of deviation of the structure with respect to the perfect cubic arrangement. Fig. 2 illustrates the crystalline structure adopted by the material, where it can be clearly seen that the Y-O6 and Sb-O6 octahedra evidence significant size differences because the ion radii of the cations of Y3+ and Sb5+ are 35% different from each other. In view of the above, the distances of the links Y-O (2.220 ± 0.001 Å) are 10.5% greater than the distances in the Sb-O links (1.987 ± 0.001 Å). Meanwhile, inclinations or rotations in the octahedra are not observed because the distances in the BaO bonds always remain constant with a value of 2.977 ± 0.001 Å, so the structure remains cubic. It is for these reasons that Fig. 2 shows a stack formed by the larger octahedra (Y-O6), which contain the smallest octahedra (Sb-O6) interspersed. On the other hand, these small differences produce a τ slightly less than 1.0, but without affecting the cubic structure of the material.

Fig. 2.

Structural arrangement for the Ba2YSbO6 in the Fm 3¯ m space group.

4.2Surface microstructure and composition

The representative surface morphology of the samples of Ba2YSbO6 is shown in Fig. 3, in images for the configurations of backscattered electrons (a) and secondary electrons (b), with a magnification of 16,000×. The granular surface topography of the material observed in Fig. 3 suggests the occurrence of a random distribution of grains of different sizes and polyhedral shapes. Measurements (inset of Fig. 3) of grain sizes using the intercepts method revealed that the length of their equatorial axes varies from 0.2 μm in the smallest to about 1.0 μm in the largest. The variety in the size of the grains, as well as the evidence of porosity and of cavities with submicrometric dimensions on the surface, suggest that a longer time or temperature may have been missing during the thermal sintering process to ensure greater interdiffusion and densification of the grains in the material.

Fig. 3.

SEM image of the surface topology for the Ba2YSbO6 perovskite-like material.


In order to semiquantitatively establish that the composition of the experimentally produced material corresponds to that expected from the stoichiometry proposed for a sample of Ba2YSbO6, a compositional analysis was carried out by EDX spectra, such as the one that is presented in Fig. 4. This study was conducted, focusing the incidence of the X-ray beam generated by a Bruker cannon on various surface regions of the sample. The observed peaks correspond to energetic emissions due to transitions between orbital M-L (Lα) and L-K (Kα and Kβ), with energy values that reveal only the occurrence of energy lines related to transitions between the electronic layers of Ba, Y, Sb and O, which allow to establish that there are no impurities based on other atoms but only those expected from the oxide precursors used. After integrating the curve, eliminating the background and peak deconvolution, it was possible to obtain the percentages by weight of the component atoms of the compound, as shown in Table 2. As expected, according to Fig. 4 and Table 2, the highest peak corresponds to the largest fraction by weight in the sample, i.e., Ba. It is followed by Sb and Y, whose value is close to that of O. The obtained values are compared with those theoretical values expected from the stoichiometry of the material.

Fig. 4.

EDX spectrum obtained for the Ba2YSbO6 double perovskite.

Table 2.

Experimental and expected weight percentage for the Ba2YSbO6 material obtained from the deconvolution of the EDX spectrum.

Element  Experimental weight (%)  Experimental weight (%)  Difference (%) 
Ba  46.42  47.25  1.75 
21.34  20.95  1.86 
Sb  15.93  15.30  3.95 
15.81  16.51  4.24 

The differences between the values of experimental weight percentage (obtained by means of EDX) and theoretical values take place because oxygen is a very light element and the X-ray scattering technique used does not apply continuous radiation, for which it presents difficulties in the resolution for this type of elements. For this reason, after making a correction of the average atomic number of the sample, it is possible to affirm that the composition of the material is close to that expected from its chemical formula given by Ba2YSbO6. This result corroborates the statement made from the structural characterization that the compound possesses a single crystallographic phase.

4.3Magnetic response

In order to evaluate the magnetic response of the material, measurements of magnetization DC as a function of temperature under the application of magnetic field strengths H = 0.2, 0.5, 2.0, 10, 20 and 30 kOe were carried out in the range of temperature between 50 and 325 K, following the Zero Field Cooled (ZFC) and Field Cooled (FC) procedures. Fig. 5 shows the results of magnetization in the presence of low fields H = 0.2, 0.5 and 2.0 kOe. As observed in the picture, for low external fields, despite the occurrence of cationic arrangement discussed in section 4.1, a marked irreversible trend takes place, such that the separation between ZFC and FC behavior seems to increase when the value of the applied field is augmented. The ZFC curves are characteristic of a system where the freezing of magnetic moments takes place, which at low temperatures are randomly arranged, with a net value of the magnetization because a certain number of moments is aligned in the direction of the external field. The increase in temperature breaks some correlations between magnetic domains, subtly decreasing the net value of the magnetization. This behavior is observed in both the ZFC and the FC curves. However, in the temperature range between 100 and 125 K, the magnetization increases abruptly, and then decays approximately with the inverse of the temperature. As we will see later, throughout the temperature regime that was studied, the material shows a character of ferromagnetic type in the presence of low magnetic fields. Thus, the anomaly that occurs in the magnetic response, at T ≈ 118 K, which is manifested through an increase in the magnetic moment of the material, can be seen as a spontaneous reentrance of the preferential arrangement of the ferromagnetic domains in the direction of application of the external magnetic field. This anomaly can be associated with the occurrence of a phase transition that takes place at this temperature value, which manifests itself differently, depending on the measurement procedure. Meanwhile, following the two recipes, ZFC and FC, in the range 50 K < T < 80 K a decrease in magnetization is observed with the increase in temperature, much more marked in the FC curve than in the ZFC because in the last one, the effects of the freezing prior to the application of the field affect in a singular way the response of the system. For this reason, we will limit the analysis to the curve corresponding to the FC procedure, where the reentrant ferromagnetic behavior that takes place at T = 118 K could be caused by the rupture of the antiferromagnetic effect that occurs in the lower part of this transition. The antiferromagnetism in this regime could be due to the occurrence of some type of polar ordering, accompanied by octahedral distortions caused by the movement of the cations Y3+ and Sb5+, which, in principle, would produce a transition changes in the crystalline symmetry of the material, resulting in a frustrated antiferromagnetic system with presence of strongly competing antiferromagnetic interactions, which would justify the marked existence of magnetic irreversibility [32].

Fig. 5.

Low-fields magnetic susceptibility as a function of temperature measured in the Ba2YSbO6 material.


When high magnetic fields are applied (H = 10, 20 and 30 kOe), the susceptibility curves of Fig. 6 clearly show the disappearance of both the irreversibility between the ZFC and FC responses and the antiferromagnetic rupture transition observed in T = 118 K in the presence of low applied fields. This behavior takes place because the high magnetic fields cause the ferromagnetism of the system to prevail over the short-range mechanisms that give rise to the frustration and weak antiferromagnetism observed at low temperatures and low applied fields.

Fig. 6.

High-fields magnetic susceptibility as a function of temperature measured in the Ba2YSbO6 material.


Fig. 7 represents the magnetization as a function of applied fields up to 30 kOe. At low temperatures (50 K) the material exhibits a weak ferromagnetic behavior for applied fields lower than 5.0 kOe, but at high temperatures (200 K and 300 K), the hysteretic behavior prevails but is restricted to applied fields lower than 3.0 kOe, as showed in the inset of Fig. 7. Meanwhile, in the presence of fields greater than those mentioned above, the magnetization adopts an approximately linear behavior without evidence of saturation. This behavior can be due to the magnetic response of the large number of grains of submicrometric dimensions, as established in section 4.2, which could be giving a strong superparamagnetic contribution due to the high surface density that increases the total magnetic moment of the particles with respect to the individual magnetic moments at the atomic level [33]. This means that the decreasing behavior of the susceptibility with the increase in temperature (observed in Fig. 6) corresponds to the superparamagnetic tendency of the material in the high field regime, which does not detract from the ferromagnetic character of the material that is characterized by the hysteretic response observed in the inset of Fig. 7 for low magnetic fields.

Fig. 7.

Magnetization hysteresis curves for the Ba2YSbO6 perovskite.


A priori, it could be expected that the Ba2YSbO6 did not present an order of ferromagnetic type, because the Ba2+ is a non-magnetic element; Y3+ is a paramagnetic element with only one 4d1 electron available to contribute to magnetization, although its similarities with rare earths [34], attributes that could give rise to exotic properties when Y3+ acts as a substantial component of complex perovskite-type materials; and the Sb5+ is a diamagnetic element with 5p3 orbitals in its last electron shell. Additionally, as can be seen in Sections 4.4 and 4.5, Ba2YSbO6 behaves as an insulating material, which in some way contrasts with the observed ferromagnetic feature. Apparently contradictory results such as those presented here are part of the strange nature of perovskite type materials. In relation to the character of ferromagnetic insulator evidenced by the material Ba2YSbO6, this type of response has been reported in the double perovskite Ba2NaOsO6, which has been characterized as a 5d1 ferromagnetic Mott insulator, where the magnetic nature is attributed to strong spin-orbit interactions [35]. As in our case, Ba2NaOsO6 evidences a cubic structure at room temperature, but the ferromagnetic behavior is reported at temperatures below 8 K with paramagnetic feature at T > 8 K. The appearance of ferromagnetic response in an insulating material confers it potential applications in the spintronics industry such as Josephson junctures magnetic and quantum devices without dissipation, among others [36]. The type of interaction that can give rise to the observed magnetic ordering will be discussed in section 4.5.

4.4Optical band gap determination

Because one of the objectives of this paper is the theoretical study of the distribution of valence electrons around the level of Fermi, which will give information about the energy gap, among other physically relevant properties (as will be seen in the section 4.5), diffuse reflectance measurements were carried out in order to experimentally determine the value of the gap. Fig. 8a shows a diffuse reflectance curve as a function of wavelength, measured in the regime between 200 and 1000 nm with a step of 1 nm, in which the sample absorbs UV–vis-NIR radiation, producing excitations related to certain molecular vibrations inside the unit cell of the Ba2YSbO6 material. Particularly, three regions of wavelength are identified for the values λ1 = 236 nm, λ2 = 301–405 nm and λ3 = 802–997 nm, which correspond to energy values E1 = 5.25 eV, E2 = 3.06–4.13 eV and E3 = 1.24–1.56 eV. It is expected that in the double perovskites eight vibration modes take place [37], of which, five can be observed by Raman spectroscopy and three by means of UV–vis-NIR. In the diffuse reflectance spectrum of the Ba2YSbO6 material, the energy regimes obtained are closely associated with the molecular bonds and the hybridizations between electronic orbitals O2p-Ba6s, O2p-Y4d and O2p-Sb5p.

Fig. 8.

Optical response of the Ba2YSbO6 material. Fig. 9a exhibits the curve of reflectance % as a function of wave length and Fig. 9b shows the graphical determination of the energy gap through the Kubelka-Munk analysis.


The determination of the gap was made from the spectrum of diffuse reflectance by means of the analysis of the experimental data, following the method of Kubelka-Munk [38] in curves {ln[(Rmax-Rmin)/(R-Rmin)]}2 as a function of , as exemplified in Fig. 8b, where R represents the measured reflectance, Rmax and Rmin are the maximum and minimum reflectances, and is the absorbed energy. The obtained value was Eg = 4.61 ± 0.11 eV, which is typical of essentially insulating materials. This value will be analyzed later, in Section 4.5, as part of the discussion of the results of the density of the electronic states.

4.5Electronic density of states

The curve presented in Fig. 9 exemplifies the dependence of the total energy (given in eV) calculated with respect to the volume of the unit cell (in Å3 units) for the Ba2YSbO6 double perovskite. In the figure, the points are the data obtained by means of DFT, while the continuous line represents the adjustment of the energy values obtained, following the equation of state of Murnaghan [39]. The results of the adjustment suggest that the minimum energy (−56.9295 eV = −4.1842 Ry) takes place for a volume of 616.0288 Å3, which corresponds to a lattice parameter a = 8.5088 Å. This value of the cell constant is 98.9% in accordance with the experimental result obtained in Section 4.1 of this document. Bearing in mind that Murnaghan's equation of state is a relation between the volume of a system and the pressure to which it is subjected, it was possible to calculate that the bulk modulus of the material is 1.3 mbar.

Fig. 9.

Fitting to the Murnaghan equation of the data obtained by minimizing energy as a function of volume of the crystallographic cell for the Ba2YSbO6 material.


Fig. 10 is a scheme of the total density of states calculated for the valence-electrons occupation at energy levels close to the Fermi level, where E = 0 eV has been labeled as the Fermi level. As observed in the picture, a band gap Eg = 3.90 eV takes place, characterizing the insulating nature of this Ba2YSbO6 complex perovskite. This value of Eg corresponds to 85% of that value found experimentally in section 4.4, which is typical in calculations by Wien2k, with exchange and correlation potentials included by means of GGA approximation, where the value of Eg is usually underestimated [40]. The partial density of states corresponding to the Ba, Y, Sb and O contributions are presented in Fig. 11. In the valence band, far from the Fermi level, a group of very flat states, characteristic of highly localized electrons, is observed in the energy interval between −10.2 eV and −10.4 eV, which are due to the hybridization of 5px and 5py orbitals of Barium with 2 s orbitals of Oxygen with minority participation of 5p and 4d-t2g states of Yttrium. In the regime from −6.5 eV to −7.2 eV, another band of localized electrons is observed, which is due to the contribution of 5 s orbitals of Antimony and 2 s and 2p of the Oxygen. The highest electronic contributions near the Fermi level are found between −4.2 eV and 0 eV, constituted by 5p states of Antimony that are strongly hybridized with 5 s, 4p and 4d-t2g orbitals of the Yttrium through the mediation of 2 s and 2p oxygen states. Due to the symmetric character of the bands for the two electronic spin configurations (up and down) in the vicinity of the Fermi level, the effective magnetic moment resulting from the calculation is zero. Meanwhile, from the inset of Fig. 6, it is possible to infer the occurrence of a ferromagnetic moment up to 0.110 μB at T = 50 K and 0.086 μB at room temperature. This ferromagnetic moment is between 43% and 55% of the value reported for the Ba2NaOsO6 perovskite-like Mott insulator [41]. In the case of the Ba2NaOsO6, the insulating feature and the ferromagnetic response was attributed to the combined effect of electron correlation and spin-orbit coupling [42]. We interpret our exotic results following the very plausible and simple model to explain the ferromagnetic response in this type of materials as suggested by Bristowe et al. [43], which consider the occurrence of intra-site spin-exchange via Hund's rules, which would attribute unpaired spins to the orbitals 4d-t2g (dxz and dyz) of the Yttrium, mediated by the 2p orbitals of the Oxygen and 5p of Antimony, producing ferromagnetic effects in the insulating material.

Fig. 10.

Total density of states calculated for the Ba2YSbO6 double perovskite by considering both up and down spin polarizations. The Fermi level corresponds to E = 0 eV.

Fig. 11.

Partial density of states calculated for up and down spin polarizations. Figures a, b, c and d show the partial contributions of Ba, Y, Sb and O respectively. In this representation the Fermi level is located at the zero energy value. The arrows identify the states of spin up and down.


Structural characterization through the Rietveld refinement of experimental X-ray diffraction data in solid-reacted samples of Ba2YSBO6 reveals its majority crystallization in a complex cubic structure belonging to the Fm3¯m (# 225) space group, with cell parameter a = 8.4182(0) Å, presenting size differences between the Y-O6 and Sb-O6 octahedrons, which cause a small decrease in the tolerance factor with respect to the unit, which is the value corresponding to an ideal cubic double perovskite. The SEM surface images show a granular topography composed by grains of submicrometric mean size and the EDX spectrum indicates that the obtained composition of the synthesized material is in agreement with the stoichiometry of the chemical formula. The magnetic response suggests the occurrence of ferro-type magnetic ordering at room temperature and at low temperatures, with evidence of irreversibility in the presence of low magnetic fields, as well as an antiferromagnetic reentrance observable at T = 118 K for fields applied up to 2.0 kOe. These anomalies are attributed to possible polar ordering with probable strongly competing antiferromagnetic interactions and distortions of the different Y-O6 and Sb-O6 octahedra. Optical band gap measurements allowed to establish the insulating character of the Ba2YSbO6 double perovskite with Eg = 4.61 eV, which was corroborated through calculations of density of electronic states in the vicinity of the Fermi level. The ferromagnetic feature of this insulating material allows characterizing it as a 4d1 ferromagnetic Mott insulator. Based on the literature, we suggest that this type of response takes place because there is an intra-site spin-exchange as a consequence of unpaired spins in the Y-4d-t2g orbitals, with intermediation of the O-2p and Sb-5p orbitals.

Conflicts of interest

The authors declare no conflicts of interest.


This work was partially supported by Division of Investigation and Extension (DIEB) of the National University of Colombia and Administrative Department of Science and Technology Francisco José de Caldas - COLCIENCIAS, on the project FP80740-243-2019. Two authors (JA Cuervo Farfán and JA Cardona Vasquez) are part of the scholarship program for national PhD studies (COLCIENCIAS).

S. Vasala, M. Karppinen.
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