Geometrical frustration and piezoelectric response in oxide ferroics

We show that their increased piezoelectric response is primarily due to a geometrical frustration in the underlying perovskite lattice induced by local fluctuations in the tilt pattern of the constituent niobium-oxygen octahedra, and not to a crystal-crystal phase transition or distinct nanodomains

Valeri Petkov; Jong-Woo Kim; Sarvjit Shastri; Shashaank Gupta; Shashank Priya

2020

Scholarcy highlights

  • Materials with increased functionality are often based on crystalline structures with significant local disorder
  • The exact structural origin of the increased piezoelectric response of oxide ferroics is still unclear. Evoked models attribute it to emerging polar nanoregions inside a nonpolar matrix, the existence of a morphotropic boundary separating polar phases with different crystallographic symmetry, low-symmetry bridging phases facilitating polarization rotation, and displacive and order-disorder structural phase transitions
  • We use both conventional and resonant high-energy x-ray diffraction coupled to atomic pair distribution function analysis and three-dimensional computer simulations to examine the relationship between the local structure and piezoelectric properties of exemplary sodium-potassium niobate ferroics
  • We show that their increased piezoelectric response is primarily due to a geometrical frustration in the underlying perovskite lattice induced by local fluctuations in the tilt pattern of the constituent niobium-oxygen octahedra, and not to a crystal-crystal phase transition or distinct nanodomains
  • Based on the experimental data and model calculations involving Goldschmidt's tolerance factor for the stability of perovskites, we show that the fluctuations are driven by the mismatch between the radii of sodium and potassium atoms, and the increased piezoelectric response of sodium-potassium niobates scales with the variance in the distribution of these radii about the average value
  • Contrary to the case of KNbO3, the Nb−O6 octahedra in NaNbO3 are tilted with respect to each other
  • Right: Our experimental data from the respective plots on the left as fit with a second-degree polynomial function of the type 〈rA(x)〉+x(x+1)(rK−rNa)2

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