Anharmonic thermal vibration in a crystal of lithium(I) tantalum(V) trioxide, LiTaO₃

Abstract

The electron-density distribution in a crystal of LiTaO₃ has been investigated with the single-crystal X-ray diffraction method. The crystal has the cell dimensions a=5.15329(7) and c=13.7806(5) Å with the space group R3c and Z=6. Residual electron densities due to anharmonic thermal vibration were observed around the Ta⁵⁺ ion. Refinement with anharmonic thermal parameters improved the coincidence of the observed and calculated structure factors significantly. The C₃₃₃ (the coefficient of Δz³) value of Ta⁵⁺ is most significant among the third and fourth order anharmonic potential parameters. It has revealed that significant errors are sometimes introduced into positional parameters if contributions of odd order terms of anharmonic potentials are ignored.