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The crystal structure of visible light absorbing piezoelectric semiconductor SrNb2V2O11 revisited: High-resolution X-ray diffraction, vibrational spectroscopy and computational study

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Gumeniuk,  Roman
Roman Gumeniuk, Chemical Metal Science, Max Planck Institute for Chemical Physics of Solids, Max Planck Society;

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Citation

Odynets, I. V., Khainakov, S., Garcia-Granda, S., Gumeniuk, R., Zschornak, M., Soloviova, N., et al. (2019). The crystal structure of visible light absorbing piezoelectric semiconductor SrNb2V2O11 revisited: High-resolution X-ray diffraction, vibrational spectroscopy and computational study. Journal of Materials Chemistry C, 7, 5497-5505. doi:10.1039/c9tc00410f.


Cite as: http://hdl.handle.net/21.11116/0000-0003-BD18-E
Abstract
Ferroelectric materials have a long-term track record of applications in electronics due to their spontaneous electric polarization. This property can be coupled with photoabsorption properties, resulting in a bulk photoelectric effect, the new on-the-edge domain for ferroelectric use. In this sense, considering the low bandgap of binary strontium-niobium ortho-vanadate SrNb 2 V 2 O 11 , which has recently been reported as ferroelectric, we propose here a deep experimental and computational understanding of its structural and physical properties, considered relevant for further applications. Microcrystalline SrNb 2 V 2 O 11 was prepared by a conventional solid state route, proposing a synthetic pathway deduced from thermoanalytical observations and high-temperature powder X-ray diffraction. The crystal structure (space group Cc, a = 18.15415(2) Å, b = 5.52811(6) Å, c = 9.52728(1) Å, β = 99.8033(8)°, Z = 2), successfully solved using high resolution powder X-ray diffraction, reveals the presence of distorted perovskite-like [Nb 4 V 2 O 12 ] units when preparing [Nb 2 V 2 O 11 ] sheets. By application of symmetry adapted mode analysis, the non-centrosymmetry originates from Sr atom displacements and [Nb 4 V 2 O 12 ] unit "breathing" deformations, which can be explained in terms of the group-subgroup relationship. By ground state analysis of the polytypes across possible C-centered monoclinic cells, only the present experimentally based structural model (space group Cc) can be adopted, substituting the so far reported crystallographic data. The semiconducting nature of the phase, with a direct bandgap of 2.3 eV, was determined by optical absorption measurements and confirmed computationally. By coupling Raman spectroscopy and density functional perturbation theory, the dielectric properties (ϵ riso = 55) were accurately calculated and the observed optical phonons were fully interpreted. Finally, using the Berry phase formalism, we predicted a value of spontaneous polarization of 16.6 μC cm -2 in the absence of confident existing experimental data. © The Royal Society of Chemistry.