REFINEMENT OF THE PbMg1/3Nb2/3O3 STRUCTURE AT LOW TEMPERATURES
A.R.Lebedinskaya, M.F.Kupriyanov
Rostov State University, Zorge 5, Rostov on
Don, 344090, Russia
The aim of present work is the analis of the PMN structure evolution at low temperatures.
The single crystal strycture of PbMg1/3Nb2/3O3 (PMN) at 103, 183 and 293 K using X-ray diffractometer (Nonius CAD-4, MoKa - radiation, sin q/l<1.01 A-1) was determined.
Total number of reflections : 1160 ( 103 K), 1161 ( 183 K), 1518 (293 K).
It was found that structural amplitudes (after their corrections) at room temperature well conform to model [1]. In studied crystal the effects of superstructure [2,3] was not found.
Debye-Waller factors were determined for Pb, Mg/Nb and O ions in PMN in these temperatures. It was found that B(Pb)>B(O)>B(Mg/Nb).
At low temperatures PMN has cubic cell ( with due regard for accuracy of experiment). For this the structural amplitudes with non - zero index l have strong quantitative changes wich interpret as effects of small disorder shifts of Pb atoms along [001] directions.
We suppose the existence of anisotropic thermal fluctuations of Pb ions in PMN about ideal positions in these conditions.
The syntheses of electron densities permitted
to obtain more precise models of PMN at low temperatures. The
received cards of distribution of electronic density permit to
assume availability at Pb atoms of random displacement preferably
along [001] direction too.
Referenses.
1. Verbaere et al. Mat. Res Bull. 1992, Vol. 2, 1227.
2. Vakhrushev S. et al. J. Phys. Chem. Solids. 1996, Vol. 57, 1517.