Synthesis of NdSc3(BO3)(4) single crystals and study of its structure properties

Using the group method, single crystals of NdSc3(BO3)4 are grown from a melt solution and X-ray structural studies are performed. It is shown that at room temperature the NdSc3(BO3)4 crystal has a huntite-type structure with space group P3121. The temperature dependence of the heat capacity shows anomalous behaviour at Т = 504 ± 1 K. This anomaly corresponds to a structural phase transition from R32 to P3121. It is known that a similar transition occurs in RFe3(BO3)4 crystals; an anomaly in the specific heat is also observed. Theoretical calculations are carried out from the first principles of the lattice dynamics of the crystal under study in a high-symmetry phase with the R32 space group. An unstable (soft) mode in the boundary point of Brillouin zone was found. It was determined that this structural instability is responsible for the structural displacement-type phase transition R32 → P3121.