Theoretical investigation of twin boundaries in WO3 : Structure, properties, and implications for superconductivity

Abstract

We present a theoretical study of the structure and functionality of ferroelastic domain walls in tungsten trioxide, WO 3. WO 3 has a rich structural phase diagram, with the stability and properties of the various structural phases strongly affected both by temperature and by electron doping. The existence of superconductivity is of particular interest, with the underlying mechanism as of now not well understood. In addition, reports of enhanced superconductivity at structural domain walls are particularly intriguing. Focusing specifically on the orthorhombic β phase, we calculate the structure and properties of the domain walls both with and without electron doping. We use two theoretical approaches: Landau-Ginzburg theory, with free energies constructed from symmetry considerations and parameters extracted from our first-principles density functional calculations, and direct calculation using large-scale, GPU-enabled density functional theory. We find that the structure of the β-phase domain walls resembles that of the bulk tetragonal α 1 phase, and that the electronic charge tends to accumulate at the walls. Motivated by this finding, we perform ab initio computations of electronphonon coupling in the bulk α 1 structure and extract the superconducting critical temperatures, T c , within Bardeen-Cooper-Schrieffer theory. Our results provide insight into the experimentally observed unusual trend of decreasing T c with increasing electronic charge carrier concentration.

Transition Temperature of Superconductivity in Sodium Tungsten Bronze -Theoretical Study Based on First-principles Calculations-

“…The result indicates that the difference in λ between WO RBA− 3 and NaWO RBA+ 3 is very small. λ increase with decreasing x, which is roughly similar to the result obtained by Mascello et al 28) The figure also shows that −µ * increases with decreasing x, and its rate of change is almost the same as that of λ. This means that the plasmon effect described by µ * plays as important role in the superconductivity of Na x WO 3 as the phononmediated attraction described by λ.…”

Superconductivity from energy fluctuations in dilute quantum critical polar metals

“…In a broader context, energy fluctuations are ubiquitous at quantum critical points, and may thus play a role in electron pairing in many settings. One instance is the case of superconductivity occurring close to a nonpolar structural transition, driven by a phonon at a high-symmetry point, exemplified by tungsten bronze [60][61][62] and the A15 compounds 63 . As in a polar metal, the critical phonon decouples from electrons at low momenta, raising the intriguing possibility of energy-fluctuation pairing.…”

Underlying physics and chemistry of ferroic-photocatalysis: a critical review

“…[50][51][52] Similarly, the presence of domain boundaries in ferroelastic materials like BiVO 4 and WO 3 signies their importance in photocatalysis, despite being centrosymmetric in the bulk. [53][54][55] In complex domain patterns their polarity almost cancels out; however a small bias/exoelectric effect can induce a local polar nature. On a rough ferroelastic surface, local surface steps break the macroscopic inversion symmetry and on nucleation the surface produces a net polarization density despite the bulk continues to remain strictly non-polar.…”