Crystal structure, absolute configuration and characteristic temperatures of SmFe3(BO3)4 in the temperature range 11-400 K.

The crystal structure of samarium iron borate was analyzed with regard to growth conditions and temperature. The inclusion of about 7% Bi atoms in the crystals grown using the Bi2Mo3O12-based flux was discovered and there were no impurities in the crystals grown using the Li2WO4-based flux. No pronounced structural features associated with Bi inclusion were observed. The different absolute configurations of the samples grown using both fluxes were demonstrated. Below 80 K, a negative thermal expansion of the c unit-cell parameter was found. The structure of (Sm0.93Bi0.07)Fe3(BO3)4 belongs to the trigonal space group R32 in the temperature range 90-400 K. A decrease in the (Sm,Bi)-O, Sm-B, Sm-Fe, Fe-O, Fe-B and Fe-Fe distances is observed with a lowering of the temperature, B1-O does not change, B2-O increases slightly and the B2O3 triangles deviate from the ab plane. The strongest decrease in the equivalent isotropic atomic displacement parameters (Ueq) with decreasing temperature is observed for atoms Sm and O2, and the weakest is observed for B1. The O2 atoms have the highest Ueq values, the most elongated atomic displacement ellipsoids of all the atoms and the smallest number of allowed vibrational modes of all the O atoms. The largest number of allowed vibrational modes and the strongest interactions with neighbouring atoms is seen for the B atoms, and the opposite is seen for the Sm atoms. The quadrupole splitting Δ(T) of the paramagnetic Mössbauer spectra increases linearly with cooling. The Néel temperature [TN = 31.93 (5) K] was determined from the temperature dependence of the hyperfine magnetic field Bhf(T), which has a non-Brillouin character. The easy-plane long-range magnetic ordering below TN was confirmed.