Seeing the Unseen: The Structural Influence of the Lone Pair Electrons in PbWO.

Pair distribution function (PDF) analysis of the scheelite-type material PbWO reveals previously unidentified short-range structural distortions in the PbO polyhedra and WO tetrahedra not observed in the similarly structured CaWO. These local distortions are a result of the structural influence of the Pb 6s lone pair electrons. These are not evident from the Rietveld analysis of synchrotron X-ray or neutron powder diffraction data, nor do they strongly influence the X-ray PDF (XPDF).

Tetrahedra Rotational and Displacive Disorder in the Scheelite-Type Oxide CsReO.

Scheelite-type metal oxides are a notable class of functional materials, with applications including ionic conductivity, photocatalysis, and the safe storage of radioactive waste. To further engineer these materials for specific applications, a detailed understanding of how their properties can change under different conditions is required─not just in the long-range average structure but also in the short-range local structure. This paper outlines a detailed investigation of the metal oxide CsReO, which exhibits an uncommon orthorhombic pseudo-scheelite-type structure at room temperature.

Intercalated Water Drives Anomalous Thermal Expansion in the Tetragonal Zircon Structured Bismuth Vanadate BiVO Photocatalyst.

The thermal transformation of the tetragonal-zircon (tz-) to tetragonal-scheelite (ts-)BiVO was studied by in situ synchrotron X-ray diffraction, thermogravimetric analysis, and Fourier-transformed infrared spectroscopy. Upon heating, the tetragonal zircon polymorph of BiVO (tz-BiVO) transitioned to the ts-polymorph between 693-773 K. Above 773 K, single phase ts-BiVO was observed before transitioning to the monoclinic fergusonite (mf-) polymorph upon cooling.

Effect of Local Structural Distortions on Antiferroelectric-Ferroelectric Phase Transition in Dilute Solid Solutions of KNaNbO.

The fundamental principles that govern antiferroelectric (AFE)-ferroelectric (FE) transitions are not well understood for many solid solutions of perovskite compounds. For example, crystal chemical considerations based on the average Goldschmidt tolerance factor or ionic polarizability do not precisely predict the boundary between the AFE and FE phases in dilute solid solutions of alkali niobates, such as KNaNbO ( ≤ 0.02).

Tetrahedral Displacive Disorder in the Scheelite-Type Oxide RbReO.

Oxides exhibiting the scheelite-type structure are an important class of functional materials with notable applications in photocatalysis, luminescence, and ionic conductivity. Like all materials, understanding their atomic structure is fundamental to engineering their physical properties. This study outlines a detailed structural investigation of the scheelite-type oxide RbReO, which exhibits a rare long-range phase transition from 4/ to 4/ upon heating.

Understanding the Re-entrant Phase Transition in a Non-magnetic Scheelite.

The stereochemical activity of lone pair electrons plays a central role in determining the structural and electronic properties of both chemically simple materials such as HO, as well as more complex condensed phases such as photocatalysts or thermoelectrics. TlReO is a rare example of a non-magnetic material exhibiting a re-entrant phase transition and emphanitic behavior in the long-range structure. Here, we describe the role of the Tl 6s lone pair electrons in these unusual phase transitions and illustrate its tunability by chemical doping, which has broad implications for functional materials containing lone pair bearing cations.

A Local Atomic Mechanism for Monoclinic-Tetragonal Phase Boundary Creation in Li-Doped NaKNbO Ferroelectric Solid Solution.

ABO perovskites display a wide range of phase transitions, which are driven by A/B-site centered polyhedral distortions and/or BO octahedral tilting. Since heterogeneous substitutions at the A/B-site can locally alter both polyhedral distortions and/or tilting, they are often used to create phase boundary regions in solid solutions of ABO, where the functional properties are highly enhanced. However, the relationships between doping-induced atomistic structural changes and the creation of phase boundaries are not always clear.