Perovskite and Pyrochlore Modifications of Pb₂MnReO₆:  Synthesis, Structure, and Electronic Properties

Abstract

We describe the synthesis and investigations of Pb 2 MnReO 6 in perovskite and pyrochlore modifications. Both the modifications are formed at atmospheric pressure, the perovskite (I) at 550°C and the pyrochlore (II) at 600°C. Rietveld refinements of the structures using the powder XRD data show that oxide I adopts the monoclinic (P2 1 /n) double perovskite structure with partial ordering (∼72%) of Mn II /Re VI at the octahedral sites, while oxide II crystallizes in a defect-pyrochlore structure where Mn II /Re VI are disordered at the octahedral sites. The frustrated cation sublattice precludes a long-range ordering of Mn/Re in the pyrochlore structure. I is a semiconductor showing evidence for a ferrimagnetic ordering at T c ∼ 100 K, but the small saturation magnetic moment (〈S〉 ) 0.81) and the divergence between FC and ZFC magnetization data are consistent with spin-glass-like behavior and a partially ordered Mn/Re in the double perovskite structure. On the other hand, both the Curie-Weiss paramagnetism down to ∼5 K and non-Arrhenius electrical resistivity behavior of II suggest a spin-liquid/spin-glass ground state that is consistent with the frustrated cation sublattice of the pyrochlore structure.

Phase Formation and Properties in the System Bi2O3:2CoO1+x:Nb2O5

“…The observed effective moments (µ eff / mol Co) and temperature-axis intercepts (θ, K) were obtained from linear fits of the inverse susceptibility data in the temperature range 100-300 K. not unexpected given the triangular symmetry of the metal lattices which results in geometric magnetic frustration. [49][50] Pyrochlore compounds are known to exhibit a wide range of cooperative magnetic properties and, for example, are of significant interest as "spin-ice" systems. [51][52][53] …”

Synthesis of new (Bi, La)3MSb2O11 phases (M = Cr, Mn, Fe) with KSbO3-type structure and their magnetic and photocatalytic properties

“…For La containing compositions, best Rietveld fit were obtained when La was disordered at both Bi(1) and Bi (2) Atom Position Our efforts to synthesize Bi 3 MnSb 2 O 11 and Bi 3 NiSb 2 O 11 in KSbO 3 type structure were unsuccessful. Instead, pyrochlore phases (Ramesha et al 2003a, b) were obtained as revealed from their powder XRD patterns. The formation of pyrochlore phase implies that Mn is in +2 oxidation state (instead of +3) corresponding to the chemical formula, Bi 2 Mn 0·67 Sb 1·33 O 7 .…”

High-pressure synthesis, structural and complex magnetic properties of the ordered double perovskite Pb2NiReO6

“…Another member of the Pb 2 MReO 6 series, e.g. Pb 2 MnReO 6 , was also studied 24 . This double perovskite crystallized with monoclinic symmetry (S. G. P2 1 /n) and shows a T C ∼ 100 K and semiconducting properties.…”