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

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.