LOCAL DISTORTIONS IN THE BIO6-OCTAHEDRA SUBLATTICE OF BAPBXBI1-XO3 ASSEEN BY BA-137 NMR NQR/

The Ba-137 NMR and NQR spectra as well as the spin-lattice relaxation rate were measured for the first time in the BaPbxBi1-xO3 samples with x = 0.9l(normal metal), x = 0.75 (superconductor) and x = 0.64 (semic onductor). The strong quadrupole broadening of the NMR lines with lowe ring temperature was found for all the samples. An evolution of static distortions in the BiO6-octahedra sublattice along with asymmetry of the electric field gradient at the Ba-sites is discussed. This asymmet ry caused by the nearest non-cubic surrounding of barium is originated from the temperature dependent tilt of BiO6-octahedra. Spin-lattice r elaxation rate of Ba-137 is monitored by fluctuating part of electric field gradient at the Ba-site and its exponential growth at low temper atures evidences the thermally activated collective rotations of BiO6- octahedra around their static tilt. An activation energy and a strengt h of these dynamic distortions are evaluated and found to increase in going from metallic to semiconducting phase of BaPbxBi1-xO3.