The crystal structure of visible light absorbing piezoelectric semiconductor SrNb2V2O11 revisited: high-resolution X-ray diffraction, vibrational spectroscopy and computational study. Issue 18 (18th April 2019)

• Record Type: Journal Article
• Authors: Odynets, Ievgen V.; Khainakov, Sergiy; Garcia-Granda, Santiago; Gumeniuk, Roman; Zschornak, Matthias; Soloviova, Natalia; Slobodyanik, Nikolay S.; Horcajada, Patricia; Babaryk, Artem A.
• Is Part Of: Journal of materials chemistry. Volume 7:Issue 18(2019)
• Page Start: 5497
• Page End: 5505
• Publication Date: 2019-04-18
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/c9tc00410f
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : The crystal lattice of piezoelectric semiconductor Sr2 Nb2 V2 O11 adopts Cc ordering due to Γ 2 − mode distortion. 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 SrNb2 V2 O11, 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 SrNb2 V2 O11 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 [Nb4 V2 O12 ] units when preparing [Nb2 V2 O11 ] sheets. By application of symmetry adapted mode analysis, the non-centrosymmetry originates from Sr atom displacements and [Nb4 V2 O12 ] 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.