Properties and high-pressure behavior of a ternary lead oxide Pb_2MnO_4

摘要

Pb_2MnO_4 and Sr-doped Pb_2MnO_4 powders have been synthesized along the Pechini process. Partial substitution of Pb~(2+) by Sr~(2+) has been effective up to 2 at%. Beyond this value, secondary phases appeared among others PbO or SrMnO_3. The effect of high pressures (<6 GPa) and high temperatures (<900 °C) on Pb_2MnO_4, containing Pb~(2+) cations with electron lone pairs, has been studied. In spite of the lone pairs present, this semiconductor (Eg = 1.5 eV) did not exhibit any phase transition under pressure. Instead, decomposition into three phases (Pb_3Mn_7O_(15), PbO and Pb_3O_4) has been observed with reduction of Mn~(4+) to Mn~(3+) and concomitant to oxidation of Pb~(2+) to Pb~(4+). Strontium doping, bearing no electron lone pair, turned out, however, to lead to the same decomposition, the one difference being a higher decomposition temperature. Electronic and thermal properties of pure and doped Pb_2MnO_4 were also investigated.