SYNTHESIS AND RESISTIVITY PROPERTIES OF SR1-XLAXPBO3-DELTA AND SRPB1-XBIXO3-DELTA

The solid solutions with the composition SrPb1-xBixO3-delta and Sr1-xL axPbO3-delta were synthesized. It was found that the solubility limits do not exceed the values x = 0.2 and x = 0.1, respectively. It was sh own by X-ray powder diffraction that the initial crystal symmetry (ort horhombic, space group Pnma) remains unchanged with the substitution, whereas unit cell parameters increase monotonically. The undoped SrPbO 3-delta exhibit positive and negative temperature coefficient of resis tivity at high and low temperatures, respectively. La-doping leads to a drastical decrease of the absolute value of the resistivity and for the doped samples with x greater than or equal to 0.05 d rho/dT is pos itive in the entire temperature range. Bi-doping leads, first to a sim ilar decrease of resistivity, but at higher substitutions, variable ra nge hopping conduction is observed. The results were interpreted in te rms of quantum interference and a subsequent transition to localized e lectronic states. (C) 1997 Elsevier Science Ltd.