Thermal Conductivity Investigation Of Ca9re(Vo4)(7) (Re = La, Nd, Gd) And Ca10m(Vo4)(7) (M = Li, Na, K) Single Crystals

The Ca9RE(VO4)(7) (RE = La, Nd, Gd) and Ca10M(VO4)(7) (M = Li, Na, K) single crystals have been grown by the Czochralski method. The binary vanadates are isostructural to "whitlockite" mineral (rhombohedral symmetry, R3c space group). Their thermal conductivity has been investigated in the range 50K-300K parallel to the c axis. For Ca9Gd(VO4)(7) crystals, the thermal conductivity has been investigated in the range 300K-550K also. Additionally, for the Ca10M(VO4)(7) (M = Li, Na, K) crystals the heat capacity has been studied in the temperature range 80K-300K. The character of the temperature dependence of thermal conductivity is close to that of glasses. The possible reasons of the observed features of the thermal conductivity have been analyzed. Raman spectra of Ca10M(VO4)(7) (M = Li, Na, K) crystals have been measured and discussed. The spectral lines were broad and similar to polycrystalline or amorphous solids. These crystals are expected to be suitable for application as efficient nonlinear optic and laser materials.