The crystal growth and properties of novel magnetic double molybdate RbFe 5 (MoO 4 ) 7 with mixed Fe 3+ /Fe 2+ states and 1D negative thermal expansion

• Published in: CrystEngComm 2021-05, Vol.23 (18), p.3297-3307
• Main Authors: Chimitova, O. D., Bazarov, B. G., Bazarova, J. G., Atuchin, V. V., Azmi, R., Sarapulova, A. E., Mikhailova, D., Balachandran, G., Fiedler, A., Geckle, U., Prots, Yu, Komarek, A. C., Gavrilova, T. A., Prosvirin, I. P., Yang, Yi, Lin, Zheshuai, Knapp, M., Ehrenberg, H.
• Format: Article
• Language: English
• ISSN: 1466-8033; 1466-8033
• DOI: 10.1039/D1CE00118C

Single crystals of new compound RbFe 5 (MoO 4 ) 7 were successfully grown by the flux method, and their crystal structure was determined using the X-ray single-crystal diffraction technique. The XRD analysis showed that the compound crystallizes in the monoclinic space group P 2 1 / m , with unit cell parameters a = 6.8987(4), b = 21.2912(12) and c = 8.6833(5) Å, β = 102.1896(18)°, V = 1246.66(12) Å 3 , Z (molecule number in the unit cell) = 2, R -factor (reliability factor) = 0.0166, and T = 293(2) K. Raman spectra were collected on the single crystal to show the local symmetry of MoO 4 tetrahedra, after the confirmation of crystal composition using energy dispersive X-ray spectroscopy (EDS). The polycrystalline samples were synthesized by a solid-state reaction in the Ar atmosphere; the particle size and thermal stability were investigated by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) analyses. The compound decomposes above 1073 K in an Ar atmosphere with the formation of Fe( iii ) molybdate. The thermal expansion coefficient along the c direction has the value α = −1.3 ppm K −1 over the temperature range of 298–473 K. Magnetic measurements revealed two maxima in the magnetization below 20 K, and paramagnetic behavior above 50 K with the calculated paramagnetic moment of 12.7 μB per formula unit is in good agreement with the presence of 3Fe 3+ and 2Fe 2+ in the high-spin (HS) state. The electronic structure of RbFe 5 (MoO 4 ) 7 is comparatively evaluated using X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations.