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

Abstract

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 (U eq) with decreasing temperature is observed for atoms Sm and O2, and the weakest is observed for B1. The O2 atoms have the highest U eq 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 [T N = 31.93 (5) K] was determined from the temperature dependence of the hyperfine magnetic field B hf(T), which has a non-Brillouin character. The easy-plane long-range magnetic ordering below T N was confirmed.

Crystal Structure of Bismuth-Containing Samarium Iron–Aluminium Borates Sm1−xBixFe3−yAly(BO3)4 (x = 0.05–0.07, y = 0–0.28) in the Temperature Range of 25–500 K

“…There were no structural phase transitions in Sm 0.93 Bi 0.07 Fe 2.72 Al 0.28 (BO 3 ) 4 in the 25-500 K temperature range based on lattice parameter dependencies (Figure 2a). Temperature dependencies of Sm 0.93 Bi 0.07 Fe 2.72 Al 0.28 (BO 3 ) 4 unit-cell parameters (Figure 2a) demonstrate similar behaviours to those of samarium and neodymium iron borates, which do not have structural phase transitions from the R32 space group at low temperatures but demonstrate magnetic ordering below T N = 32−33 K [32,40].…”

“…There were no structural phase transitions in Sm0.93Bi0.07Fe2.72Al0.28(BO3)4 in the 25-500 K temperature range based on lattice parameter dependencies (Figure 2a). Temperature dependencies of Sm0.93Bi0.07Fe2.72Al0.28(BO3)4 unit-cell parameters (Figure 2a) demonstrate similar behaviours to those of samarium and neodymium iron borates, which do not have structural phase transitions from the R32 space group at low temperatures but demonstrate magnetic ordering below TN = 32−33 K [32,40]. Unit-cell parameter c undergoes the most pronounced change over the 25-500 K temperature range (Figure 2a): Between 25 K and 85 K it decreases by about 0.002 Å as the temperature rises, and after that it increases steadily by about 0.028 Å from 85 K to 500 K. Unit-cell parameter a varies by no more than 0.0007 Å between 25 and 110 K and then slightly increases by about 0.006 Å from 110 K to 500 K. Unit-cell volume demonstrates the effect of negative thermal expansion, reflecting the behaviour of parameter c. Between 25 K and 85 K, the volume decreases by about 0.1 Å 3 and then increases by about 2.8 Å 3 (Figure 2a).…”

“…Structures of Sm1-xBixFe3-yAly(BO3)4 (x = 0.05-0.07, y = 0-0.28) single crystals were refined in trigonal R32 space group, Z = 3 (Table 2, Figure 4). Detailed descriptions of the crystal structures of rare-earth iron borates in this space group can be found in [14,15,32,40,52]. 2, Figure 4).…”

“…2, Figure 4). Detailed descriptions of the crystal structures of rare-earth iron borates in this space group can be found in [14,15,32,40,52]. There is one Wyckoff atomic position (3a) for (Sm,Bi) atoms, one (9d) position for (Fe,Al) atoms, two positions for boron atoms [B1 (3b) and B2 (9e)], and three positions for oxygen atoms [O1(9e), O2(9e), O3(18f)] (Figure 4).…”

“…However, using Bi 2 Mo 3 O 12 in a flux led to partial substitution of rare-earth atoms in the structures with ≈4-9% of bismuth atoms [15]. Incorporation of Bi in the RFe 3 (BO 3 ) 4 structure lowered the R32→P3 1 21 transition temperature; however, other structural features associated with bismuth addition have not been identified [29,32]. RAl 3 (BO 3 ) 4 single crystals were grown using the solution-in-melt technique, with different fluxes or annealing of precursors [21][22][23]33,34].…”