Synthesis of schafarzikite-type (PbBi)MnO4: Structural, spectroscopic, magnetic and thermogravimetric properties

Abstract

Stereochemically active lone electron pairs (LEPs) draw research attention in designing materials for given crystal-physico-chemical properties. While the 5s² LEP-containing schafarzikite (FeSb₂O₄) exhibits interesting properties, we report a new compound (PbBi)MnO₄ which is isostructural to schafarzikites, where the stereochemical activity of 6s²-LEP is served by both Pb²⁺ and Bi³⁺ cations located in a single crystallographic site. The phase pure sample has been prepared in a sealed quartz tube with a low pressure of about 1 Pa at 923 K. Both X-ray and neutron power diffraction data Rietveld refinements confirm (PbBi)MnO₄ to be crystallized in the space group P4₂/mbc. The Wang-Liebau eccentricity parameter that measures the strength of the stereochemical activity of the LEPs of the associated Pb²⁺ and Bi³⁺ cations was found to be 3.41(2)⋅10⁻⁵. Temperature dependent DC magnetic susceptibility suggests that (PbBi)MnO₄ is antiferromagnetic at T_N of 43(1) K, and the magnetic structure follows a G-type configuration determined by neutron diffraction at low-temperature. Thermogravimetric analysis demonstrates the thermal stability of the tetragonal phase. The lattice thermal expansion has been modeled for the low-temperature neutron data using a single Debye term, leading to a Debye temperature of 378(20) K. Temperature-dependent changes of some selective Raman frequencies are mainly dominated by the quasiharmonic effects over the isochoric anharmonicity below room temperature.