PREPARATION, CRYSTAL STRUCTURE, AND DIELECTRIC PROPERTIES OF NEW SOLID SOLUTIONS (Pb1-2xWx)O1+x (x ≈ 0.05) BASED ON THE TETRAGONAL FORM OF LEAD OXIDE

Single crystal X-ray diffraction (XRD), thermogravimetric, and dielectric studies are performed for single and polycrystalline samples of [(1-x)PbO + xWO(3)], 0 <= x <= 0.20, synthesized by solid phase reactions and crystallization of melts. The formation of previously unknown solid solutions based on the tetragonal form of lead oxide (alpha-PbO) - Pb1-2xWxO1+x, x asymptotic to 0.05 is observed. Single crystals of solid solutions are analyzed by XRD at 100 K and 293 K. It is found that their crystal structure isotypical to alpha-PbO is characterized by the orthorhombic space group Cmma with unit cell parameters (293 K) a = 5.510 angstrom, b = 5.570 angstrom, c = 5.301 angstrom. The main structural characteristics of solid solutions are determined. A structural model of the formation of solid solutions is established, according to which partial W substitution for Pb in alpha-PbO is accompanied by the inclusion of additional oxygen atoms to the location of lone pairs of substituted Pb2+ and the formation of vacancies in this cation sublattice. Temperature dependences of the permittivity and losses of solid solution crystals studied in the temperature range T = 80-570 K and at frequencies f = 1-1000 kHz do not have features characteristic of phase transitions.