Local distortions in the BiO<sub>6sub>-octahedra sublattice of BaPb<sub>xsub>Bi<sub>1−xsub>O<sub>3sub> as seen by a<sup>137sup>Ba NMR/NQR
- 作者：Verkhovskii ; S.V. ; Gerashenko ; A.P. ; Zhdanov ; Yu.I. ; Mikhalev ; K.N. ; Sagaradze ; I.V. ; Medvedev ; Eu.Yu. ; et. al.
- 关键词：Nuclear magnetic resonance (NMR) ; Nuclear quadrupolar resonance (NQR) ; BaPb<sub>xsub>Bi<sub>1&minus ; xsub>O<sub>3sub> ; BiO<sub>6sub>-octahedra tilting
- 刊名：Physica C
- 出版年：1997
- 期刊代码：80_09214534
- 类别：ms
- 出版时间：February 1, 1997
- 卷：274
- 期：3-4
- 页码：209-220
- 文件大小：840 K
摘要
The a<sup>137sup>Ba NMR and NQR spectra as well as the spin-lattice relaxation rate were measured for the first time in the BaPb<sub>xsub>Bi<sub>1−xsub>O<sub>3sub> samples with x = 0.91 (normal metal), x = 0.75 (superconductor) and x = 0.64 (semiconductor). The strong quadrupole broadening of the NMR lines with lowering temperature was found for all the samples. An evolution of static distortions in the BiO<sub>6sub>-octahedra sublattice along with asymmetry of the electric field gradient at the Ba-sites is discussed. This asymmetry caused by the nearest non-cubic surrounding of barium is originated from the temperature dependent tilt of BiO<sub>6sub>-octahedra. Spin-lattice relaxation rate of a<sup>137sup>Ba is monitored by fluctuating part of electric field gradient at the Ba-site and its exponential growth at low temperatures evidences the thermally activated collective rotations of BiO<sub>6sub>-octahedra around their static tilt. An activation energy and a strength of these dynamic distortions are evaluated and found to increase in going from metallic to semiconducting phase of BaPb<sub>xsub>Bi<sub>1−xsub>O<sub>3sub>.