Synthesis and characterization of mullite‐type Sn(Cr_1−xV_x)BO₄: Structural, vibrational, magnetic, and thermal properties

The susceptibility of either oxidation into Sn(IV) or disproportionation into Sn(IV) and Sn(0) limits the study of metal tin‐(II)‐borate ceramics. We report mullite‐type SnCrBO4 and SnVBO4 synthesized in sealed quartz tubes by conventional solid‐state method. X‐ray powder diffraction data Rietveld refinements confirm that both compounds are isostructural to PbMBO4 phases for M = Al, Ga, Cr, Mn, and Fe. The end‐members show a complete miscibility within the Sn(Cr1−xVx)BO4 solid solution. Both the microstructural (average crystallite size, microstrain, and degree of crystallinity) and crystal structural (metric parameters, bond lengths, polyhedral volume, and polyhedral distortion) parameters are observed with respect to the compositional x‐value. The stereochemical activity of the 5 s2 lone electron pairs of Sn2+ cations has been measured by using the Wang–Liebau eccentricity parameter. The structural features are complemented by 119Sn Mössbauer, Raman, and Fourier‐transformed infrared spectroscopy. The 119Sn Mössbauer isomer shifts and the quadrupole splitting values confirm the SnO4 coordination and an Sn(II) valence state. The electronic band gap has been calculated from the UV/Vis diffuse reflectance spectra, which slightly increases with successive decrease of the cationic radius from V to Cr. Temperature‐dependent inverse DC magnetic susceptibility suggests that SnCrBO4 and SnVBO4 are antiferromagnetic and ferromagnetic (FM) with a Néel temperature of 17.2(1) K and a Curie temperature of 29.8(1) K, respectively. Alike the end‐member SnVBO4, Sn(Cr0.5V0.5)BO4 is also found to be a rare FM insulator. The thermal stability decreases with increasing vanadium content in the solid solution.