Syntheses and Characterization of AM₂V₂O₁₁ (A = Ba, Sr, Pb; M = Nb, Ta) Vanadates with Centrosymmetric and Noncentrosymmetric Structures

Abstract

Five isomorphous AMVO vanadates of niobium and tantalum, namely, BaNbVO, BaTaVO, SrNbVO, SrTaVO, and PbTaVO, were prepared by solid-state reactions and structurally characterized by single-crystal and powder X-ray diffraction techniques. Barium and strontium compounds, respectively, have centrosymmetric and noncentrosymmetric types of layered structure, wherein [MVO] anionic layers are interleaved with A cations. Both types of layered structure are found for lead compound. The strontium and lead compounds are type I phase-matching materials with second-harmonic-generating efficiencies of 33-50% of LiNbO, and their dielectric properties were evaluated. A three-dimensional structural variant was also identified for strontium compounds, which crystallize in noncentrosymmetric orthorhombic space group C222.

Structural and Electronic Effect Driven Distortions in Visible Light Absorbing Polar Materials ATa2V2O11 (A = Sr, Pb)

“…Anomalies in Born charges of strontium (lead), tantalum, and structurally related oxygen atoms are similar to some of layered perovskite-type ferroelectrics, while vanadium species are inactive in the formation of the polar structure of STVO and PTVO. Calculated band gaps are found to be consistent with experimental data of ref ( 11 ), although these are relatively far from the desirable 1.3–1.6 eV for photovoltaic applications. This implies that careful doping of parental matrices with proper cations is a suitable approach to narrow the band gaps and may pave the way for further studies of bulk photovoltaic effects of tuned material.…”

“…The subtle structural distortions are intrinsic for A Ta 2 V 2 O 11 (A = Sr or Pb) due to polarized Ta–O and V–O bonds that stabilize the polar lattice of monoclinic symmetry for both compounds, in contrast to previous studies, as revealed by high-resolution X-ray diffraction. 6 , 11 , 13 The chemical type of the counter-cation, Sr or Pb in the present case, has further influence on the overall crystal packing via the local oxygen environment built up around them in a specific fashion. The atomistic view projected on studied compounds helps us to formulate several outcomes: (i) Pb 6s 2 participates in the construction of the top of valence band zone in contrast to the Sr analogue; (ii) the AMM approach allows one to detect residual V Pb interactions induced by the anisotropic behavior of the lone pair in the interior of Pb metallic centers.…”

“…Here we note that, applying a similar methodology of study to SNVO leads to excellent agreement of experimental and theoretical values. 7 , 11 Typically, BECs may be significantly higher than their expected formal charges for the ferroelectric phase of a material. For instance, Z * avg (Ta) reaches 8.34 (8.41) for STVO (PTVO), which is a quantity comparable to that reported for perovskite-type AgTaO 3 (8.87) but higher than that found for the Ruddlesden–Popper Li 2 CaTa 2 O 7 (6.12).…”

“…Full details of those investigations are summarized in the Supporting Information (see also Tables S1 and S2 and Figures S3 and S4 ). A detailed description of samples of both compounds including absorption spectra and band gaps is reported in ref ( 11 ).…”

K3V2O3F4(IO3)3: a high-performance SHG crystal containing both five and six-coordinated V5+ cations

“…Many metal vanadates featuring isolated VO 4 tetrahedron are able to display large SHG effects, such as Li 3 VO 4 (6 × KDP), LiRb 2 VO 4 (5 × KDP) and SrTa 2 V 2 O 11 (0.5 × LiNbO 3 ). [30][31][32] Interestingly, K 3 V 5 O 14 (100 × α-SiO 2 ) contains a 2D [V 5 O 14 ] 3 ˉ layer involving both VO 4 and VO 5 groups. 33 Moreover, introducing the V 5+ cation into metal iodate might achieve large SHG effects, hence the vanadyl iodates are an ideal materials class for the exploration of SHG crystals.…”