Influence of thermal prehistory on the electrical properties of tungstate crystals

 

Chem. Met. Alloys 4 (2011) 72-76

 

V.N. SHEVCHUK, I.V. KAYUN

 

Temperature- and time-induced changes of electric and dielectric parameters of AWO4 (A = Cd, or Pb) single crystals were studied experimentally. The dielectric properties measured along the [001] direction in PbWO4 single crystals (scheelite structure type) show a quasi-periodicity at about 20 h of free relaxation. A connection of this quasi-periodicity with structural and point defects dynamics, their interactions and the creation/rebuilding of complex defects (duration of the relaxation processes), is proposed. The main role in these phenomena is attributed to oxygen and lead vacancies. No thermodielectric effects were observed for CdWO4 (wolframite structure type) perpendicular to the cleavage face (010) up to 500 K.

 

 

Perspective view of the crystallographic unit cells of PbWO4 (a) and CdWO4 (b). Some elements of the structure are presented inside the unit cells. The hkl-indexes label the corresponding slip planes. The intersections of the planes are depicted by the AB, AC, and AD lines. The external electric dc field was applied parallel to the vector E.

 

Keywords

Tungstate crystal / Dielectric properties / Lattice defects / Relaxation