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Instruments / Technical Area	Publication Details	Published	Actions
I11-High Resolution Powder Diffraction	Structural origins of dielectric anomalies in the filled tetragonal tungsten bronze Sr2NaNb5O15 Jeremiah P. Tidey , Urmimala Dey , Ana M. Sanchez , Wei-Tin Chen , Bo-Hao Chen , Yu-Chun Chuang , Maria T. Fernandez-Diaz , Nicholas C. Bristowe , Richard Beanland , Mark S. Senn Communications Materials 5 DOI: 10.1038/s43246-024-00508-1 Diamond Proposal Number(s): [25166] Open Access Show Abstract ▼ Abstract: The tetragonal tungsten bronze, Sr2NaNb5O15, shows promise for application in high-temperature high-efficiency capacitors vital for the sustainable energy revolution. Previously, the structural complexity of this and related materials has obscured the mechanisms underpinning two large anomalies in relative permittivity (εr) which give rise to their exceptionally broad dielectric response. Here, we comprehensively investigate the structural evolution from −173 to 627 °C, combining electron, X-ray and neutron diffraction, electron microscopy, and first principles electronic structure calculations to unambiguously identify the structural origins of both anomalies. The peak in εr at 305 °C is associated with a polar-nonpolar phase transition, wherein cations displace along the c axis. Guided by DFT, we identify a further transition upon cooling, associated with the second peak at −14 °C, linked to the softening of an in-plane polar distortion with a correlation length limited by ferroelastic nano-domains arising from rigid-unit-like tilting of NbO6 octahedra at high temperature, imparting relaxor-like behaviour. Thus, the two dielectric anomalies in Sr2NaNb5O15 are associated with two distinct crystallographic phase transitions and their interplay with a microstructure that arises from a third, non-polar structural distortion. Chemical control of these will enable development of tuneable materials with dielectric properties suitable for high-temperature energy storage applications.	May 2024
I19-Small Molecule Single Crystal Diffraction	Pronounced interplay between intrinsic phase-coexistence and octahedral tilt magnitude in hole-doped lanthanum cuprates Jeremiah P. Tidey , En-Pei Liu , Yen-Chung Lai , Yu-Chun Chuang , Wei-Tin Chen , Lauren J. Cane , Chris Lester , Alexander N. D. Petsch , Anna Herlihy , Arkadiy Simonov , Stephen M. Hayden , Mark Senn Scientific Reports 12 DOI: 10.1038/s41598-022-18574-1 Diamond Proposal Number(s): [27647] Open Access Show Abstract ▼ Abstract: Definitive understanding of superconductivity and its interplay with structural symmetry in the hole-doped lanthanum cuprates remains elusive. The suppression of superconductivity around 1/8th doping maintains particular focus, often attributed to charge-density waves (CDWs) ordering in the low-temperature tetragonal (LTT) phase. Central to many investigations into this interplay is the thesis that La1.875Ba0.125CuO4 and particularly La1.675Eu0.2Sr0.125CuO4 present model systems of purely LTT structure at low temperature. However, combining single-crystal and high-resolution powder X-ray diffraction, we find these to exhibit significant, intrinsic coexistence of LTT and low-temperature orthorhombic domains, typically associated with superconductivity, even at 10 K. Our two-phase models reveal substantially greater tilting of CuO6 octahedra in the LTT phase, markedly buckling the CuO2 planes. This would couple significantly to band narrowing, potentially indicating a picture of electronically driven phase segregation, reminiscent of optimally doped manganites. These results call for reassessment of many experiments seeking to elucidate structural and electronic interplay at 1/8 doping.	Aug 2022

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