The vibrational spectra of lithium niobate, barium sodium niobate and barium sodium tantalate
TL;DR: In this paper, the anomalous tantalum compound has a spectrum compatible with a similar structure and the vibrations are classified as internal modes of the Mo6 octahedron (M=Nb, Ta) and lattice translations involving motion of the cation.
Abstract: Crystallographic studies of Ba2 NaNb5O15 have shown that the possible space groups are D62, C112v and D192h. The coincidences between the infrared and Raman spectra support the conclusion, based on the ferroelectric properties of the crystal, that the space group is C112v. The anomalous tantalum compound has a spectrum compatible with a similar structure. The vibrations are classified as internal modes of the Mo6 octahedron (M=Nb, Ta) and lattice translations involving motion of the cation. Force constants are calculated for internal modes using the Wilson FG matrix method and for lattice modes using the Born-von Karman theory.
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TL;DR: The phase transition behavior and composition-dependent piezoelectric properties of (NaK)(NbSb)O3−LiTaO3-BaZrO3 (NKNS-LT-BZ) pseudoternary system were investigated in this paper.
Abstract: The phase transitional behavior and composition-dependent piezoelectric properties of (NaK)(NbSb)O3–LiTaO3–BaZrO3 (NKNS–LT–BZ) pseudo-ternary system were investigated. A composition–temperature phase diagram was generalized within a certain range of BZ content in which a rhombohedral–tetragonal (R–T ) ferroelectric phase boundary connecting orthorhombic and cubic phase zones is formed near room temperature between two trifurcate points. Piezoelectric and electromechanical properties of NKNS–LT–BZ ceramics exhibit optimum values of d33=365 pC/N and kp=45% in the vicinity of the R–T phase coexistence zone. The dielectric and ferroelectric properties and the phase transition of NKNS–LT–BZ ceramics were discussed from a crystallographic point of view.
206 citations
TL;DR: In this paper, the authors measured the Raman spectra of K2O-Nb2O5-SiO2 glasses to compare the coordination state of Nb5+ ions in gallate glasses with that in silicate glasses.
Abstract: Raman spectra of K2O-Nb2O5-SiO2 glasses are measured in order to compare the coordination state of Nb5+ ions in gallate glasses with that in silicate glasses. It is found that less-distorted NbO6 octahedra with no non-bridging oxygens as well as NbO6 octahedra with non-bridging oxygens and/or with much distortion are present in the K2O-Nb2O5-SiO2 glasses. The Raman band in the 800 to 900 cm−1 region is attributed to the NbO6 octahedra with non-bridging oxygens and/or with much distortion. The broad bands in the 600 to 800 cm−1 region are attributed to less-distorted NbO6 octahedra with no non-bridging oxygens. An increase in the molar ratio Nb2O5/K2O leads to an increase in the oxygens shared by more than two polyhedra and/or a decrease in non-bridging oxygens for the NbO6 octahedra which possess non-bridging oxygens, or to an increase of distortion for much-distorted NbO6 octahedra. At the same time, an increase in the molar ratio Nb2O5/K2O increases the less-distorted NbO6 octahedra with no non-bridging oxygens. In short, GaO4 tetrahedra and NbO6 octahedra compete to attract alkali ions in gallate glasses but such competition is not found in silicate glasses.
113 citations
TL;DR: In this paper, a UV/vis absorption study was conducted for K 0.50Na0.50NbO3 nanorods, two interband transitions from O2p electron states to empty Nb4d electron states and two intraband transitions in relation to Nb5+ cations were revealed, and the band gap was about 3.09 eV.
Abstract: (K1−xNax)NbO3 (KNN) nanomaterials with various morphologies, including nanorods, step-like structures etc. were synthesized through a hydrothermal route. For KNN nanomaterials, the phase structures changed from orthorhombic to monoclinic as the x value increased from 0.27 to 0.66. Oriented attachment and aggregation are the major formation mechanism of the nanorods and the step-like structures, respectively. The compositional change in KNN induced a series of shifts of the Raman bands, of which the mechanisms are briefly discussed. A UV/vis absorption study shows that, for K0.50Na0.50NbO3 nanorods, two interband transitions from O2p electron states to empty Nb4d electron states and two intraband transitions in relation to Nb5+ cations are revealed, and the band gap is about 3.09 eV.
110 citations
TL;DR: The structure of potassium niobium silicate glasses in a wide compositional range has been studied by means of Raman and FTIR spectroscopy as mentioned in this paper, and it was found that the structure of such glasses is formed by SiO 4 tetrahedra and distorted NbO 6 octahedra.
Abstract: The structure of potassium niobium silicate glasses in a wide compositional range has been studied by means of Raman and FTIR spectroscopy. The glasses spectra were compared to those of the KNbSi 2 O 7 and K 3 Nb 3 O 6 Si 2 O 7 polycrystalline samples, obtained by crystallization of glasses of the same composition. It was found that the structure of such glasses is formed by SiO 4 tetrahedra and distorted NbO 6 octahedra. The amount of highly distorted (edge-sharing, non-bridging oxygens) octahedra results essentially unchanged from the glass composition. By contrast, the fraction of octahedra with a lower distortion degree (corner-sharing, bridging oxygens) increases with the Nb 2 O 5 content. Raman and FTIR investigations indicate that during long heat treatments at temperatures near T g , in the 23K 2 O · 27Nb 2 O 5 · 50SiO 2 glass, a structural change occurs regarding the amorphous matrix with a decrease of the niobium octahedra distortion. This can be related to a segregation process producing niobium rich regions nanometric in size. In the first heat treatment (2 h) the glass remains amorphous while for more prolonged heat treatments, nanocrystals of an unidentified phase are formed. In the same time the changes of the amorphous matrix hinder further crystallization.
92 citations
TL;DR: The results rationally expand the feasibility of the developed NCG toward applications in lightweight, diminutive, and multifunctional rollable or wearable electronic devices and can potentially be used to scavenge biomechanical energy from low-frequency human motions.
Abstract: A fully rollable nanocomposite-based nanogenerator (NCG) is developed by integrating a lead-free piezoelectric hybrid layer with a type of nanofiber-supported silver nanowire (AgNW) network as electrodes. The thin-film nanocomposite is composed of electroactive polyvinylidene fluoride (PVDF) polymer matrix and compositionally modified potassium sodium niobate-based nanoparticles (NPs) with a high piezoelectric coefficient (d33) of 53 pm/V, which is revealed by the piezoresponse force microscopy measurements. Under periodical agitation at a compressive force of 50 N and 1 Hz, the NCG can steadily render high electric output up to an open-circuit voltage of 18 V and a short-circuit current of 2.6 μA. Of particular importance is the decent rollability of the NCG, as indicated by the negligible decay in the electric output after it being repeatedly rolled around a gel pen for 200 cycles. Besides, the biocompatible NCG can potentially be used to scavenge biomechanical energy from low-frequency human motions, a...
92 citations
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TL;DR: In this article, a general rule for writing down the coefficients of the transformation to symmetry coordinates is derived together with a method of obtaining the kinetic energy reciprocal matrix (G) in terms of symmetry coordinates with a minimum of algebra.
Abstract: Developments which reduce the labor of calculating the vibration frequencies of complex molecules are described. In particular a vectorial scheme is given for obtaining the reciprocal of the matrix of the kinetic energy in terms of valence‐type coordinates. A general rule for writing down the coefficients of the transformation to symmetry coordinates is derived together with a method of obtaining the kinetic energy reciprocal matrix (G) in terms of symmetry coordinates with a minimum of algebra. A treatment of redundant coordinates is developed. In addition, reduction of the secular equation by the splitting out of high frequencies, a new type of isotope product rule, and the determination of normal coordinates are discussed. The molecule CH3Cl is worked out as an illustration.
685 citations
TL;DR: In this paper, a method for obtaining the secular equation for the vibration frequencies of a molecule directly in expanded form, i.e. as an algebraic rather than a determinantal equation, is described.
Abstract: A method is described for obtaining the secular equation for the vibration frequencies of a molecule directly in expanded form, i.e. as an algebraic rather than a determinantal equation. The force constants occur literally and the masses may occur either literally or numerically, as desired. The symmetry may be employed as usual to factor the secular equation. Several methods of obtaining approximate roots are described for which the expanded form is particularly suitable. Finally, an example, the nonlinear general triatomic molecule, is worked out algebraically.
651 citations
TL;DR: The Ferroelectric Ba0.27Sr0.75Nb2O5.78 as discussed by the authors is a tungsten bronze-type structure crystallizing in the tetragonal system, with lattice constants a = 12.43024
Abstract: Ferroelectric Ba0.27Sr0.75Nb2O5.78, with Tc = 348° ± 15°K, is a tungsten bronze‐type structure crystallizing in the tetragonal system, with lattice constants a = 12.43024 ± 0.00002 and c = 3.91341 ± 0.00001 A at 298°K, space group P4bm, and five formulas in the unit cell. The integrated intensities of 6781 structure factors were measured with PEXRAD, 875 symmetry‐independent structure factors being significantly above background. The metal‐atom positions were determined from the three‐dimensional Patterson function and the oxygen atoms from subsequent Fourier series. The final agreement factor between measured and calculated structure factors is 0.0508. The structure consists of close‐packed slightly puckered layers of oxygen atoms separated by nearly c / 2. The Nb atoms are slightly displaced from one layer, the Ba and Sr atoms from the other and in the same sense. The oxygen atoms in the Ba and Sr layer are disordered. Neither of the two independent sites occupied by the Ba and Sr atoms is fully filled....
570 citations
TL;DR: Ferroelectric Ba(4+x)Na(2 − 2x)Nb10O30, with a Curie temperature of 833°K, has a tungsten bronze-type structure and crystallizes in the orthorhombic system as mentioned in this paper.
Abstract: Ferroelectric Ba(4+x)Na(2 − 2x)Nb10O30, with a Curie temperature of 833°K, has a tungsten bronze‐type structure and crystallizes in the orthorhombic system, with subcell lattice constants a = 17.59182 ± 0.00001, b = 17.62560 ± 0.00005, and c = 3.994915 ± 0.000004 A at 298°K. The space group is Cmm2, and there are two formulas in the subcell. The c axis of the true cell is double that of the subcell. The integrated intensities of 6911 reflections within a reciprocal hemisphere of radius (sinθ)/λ = 1.02 A−1 were measured with PEXRAD, 1873 symmetry‐independent structure factors being significantly above background. The metal atom positions were determined from the three‐dimensional Patterson function and the oxygen atoms from metal‐phased Fourier series. The final agreement index between measured and calculated structure factors is 0.0579. The structure differs only in detail from previously determined tetragonal tungsten bronze structures. In the general formula (A1)2(A2)4C4(B1)2(B2)8O30, the B1 and B2 sites are fully occupied by Nb, the A2 sites by Ba and the A1 site by 87.0% Na and 6.5% Ba. Evidence from chemical analysis, x‐ray density calculations and the present determination suggests that the best approximation to the formula of the crystal studied is Ba4.13Na1.74Nb10O30. The Ba and O atoms at z ≃ 12 are disordered in a manner similar to the O atoms in the Ba layer in barium strontium niobate. The four crystallographically independent Nb atoms, each in octahedral coordination, are linked to O atoms by distances ranging from 1.765 ± 0.021 to 2.270 ± 0.021 A, with a mean value of 1.989 A. Ba is 10 coordinated, with Ba–O distances ranging upward from 2.671 ± 0.013 A. Na is 12 coordinated, with Na–O distances ranging from 2.660 ± 0.014 to 2.990 ± 0.015 A, with a mean of 2.788 A. The Nb‐atom displacements from the mean oxygen planes lie in the range 0.171–0.205 A; the parabolic relation with Curie temperature predicts a displacement of 0.204 A. The measured value of Ps at room temperature is 40 μC cm−2: the linear relation between displacement and polarization predicts a saturation value of 44–53 μC cm−2. All metal atoms are displaced from the oxygen planes in the sense given by the macroscopic positive polarity.
228 citations
TL;DR: Polarized Raman scattering from a crystal of LiNb${\mathrm{O}}_{3}$ has been measured at room temperature using a continuous He-Ne gas laser as a source as mentioned in this paper.
Abstract: Polarized Raman scattering from a crystal of LiNb${\mathrm{O}}_{3}$ has been measured at room temperature using a continuous He-Ne gas laser as a source. The spectra and scattering efficiencies are discussed and frequency assignments are made for three transverse ${A}_{1}$ and one longitudinal and seven transverse $E$ vibrations.
136 citations