The temperature dependence of nuclear relaxation rate, 1=T 1 has been measured for copper halides, CuX with X being Cl, Br and I. The results are interpreted in terms of the quadrupole relaxation due to lattice vibrations and defect motions. The data of 1=T 1 are compared with a model calculation based on an ionic model, in which the degree of covalent bonding 0 is estimated to be 63% for CuCl, 49% for CuBr and 27% for CuI. The 0 values for copper halides are compared with previous values for silver and sodium halides, and also compared with the ionicity of A N B 8ÀN binary compounds. The relation between 0 values and migration energies E m for cation vacancies derived from 1=T 1 data is discussed in connection with the superionicity of -AgI.
Two-pulse phonon echo measurements were performed from room temperature to 900 K in micro particles of polycrystalline and single crystalline LiNbO3 to investigate the relationship between lithium ionic diffusion and decay time, T
2, in a phonon echo study. Decay time was dependent on temperature, showing a rapid decrease above 800 K in the polycrystalline sample. The origin of this anomaly is interpreted in terms of a simple Debye-type relaxation due to lithium ionic diffusion. The activation energy, which was evaluated as 0.93 eV in the polycrystalline samples, was comparable with reported values from ionic conductivity and NMR studies. On the other hand, single crystalline LiNbO3 showed no signs of lithium ionic diffusion up to 900 K. The contribution to T
2 from lithium ionic diffusion would be dominant at higher temperatures than 900 K because of the much higher activation energy in a single crystalline sample. It is shown that phonon echo decay time is strongly connected with ionic diffusion in the particles.
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