Phonon Vibrational Modes Research Articles

Realization of Strained Stanene by Interface Engineering.

Stanene, the tin analogue of graphene, has been predicted to be a two-dimensional topological insulator, providing an ideal platform for the realization of the quantum spin Hall effect even at room temperature. Here, continuous stanene has been successfully formed on the Au(111) substrate, and its crystalline structure, phonon properties, and electronic structures are investigated by scanning tunneling microscopy and in situ Raman spectroscopy combined with first-principles calculations. The surface Sn-Au alloy with a coverage-dependent structural evolution is first identified. At coverage above a critical value, the Au-Sn alloy is gradually converted into epitaxial stanene with a √3 × √7 superstructure. Distinctive vibrational phonon modes are discovered in √3 × √7 stanene through in situ Raman spectroscopy, which are correlated with the tensile strain evoked by its singular buckled structure. Our results present clear evidence for the existence of epitaxial stanene and provide a platform for exploration of the exotic properties of this strained two-dimensional material.

Pulsed Laser Deposition of Aluminum Nitride Films: Correlation between Mechanical, Optical, and Structural Properties

Aluminum nitride (AlN) films were synthesized onto Si(100) substrates by pulsed laser deposition (PLD) in vacuum or nitrogen, at 0.1, 1, 5, or 10 Pa, and substrate temperatures ranging from RT to 800 °C. The laser parameters were set at: incident laser fluence of 3–10 J/cm2 and laser pulse repetition frequency of 3, 10, or 40 Hz, respectively. The films’ hardness was investigated by depth-sensing nanoindentation. The optical properties were studied by FTIR spectroscopy and UV-near IR ellipsometry. Hardness values within the range of 22–30 GPa and Young’s modulus values of 230–280 GPa have been inferred. These values were determined by the AlN film structure that consisted of nanocrystallite grains, strongly dependent on the deposition parameters. The values of optical constants, superior to amorphous AlN, support the presence of crystallites in the amorphous film matrix. They were visualized by TEM and evidenced by FTIR spectroscopy. The characteristic Reststrahlen band of the h-AlN lattice with component lines arising from IR active phonon vibrational modes in AlN nanocrystallites was well detectable within the spectral range of 950–500 cm−1. Control X-ray diffraction and atomic force microscopy data were introduced and discussed. All measurements delivered congruent results and have clearly shown a correlation between the films’ structure and the mechanical and optical properties dependent on the experimental conditions.

Structural dependence of microwave dielectric properties of spinel structured Mg2(Ti1-Sn )O4 solid solutions: Crystal structure refinement, Raman spectra study and complex chemical bond theory

Abstract Mg2(Ti1-xSnx)O4 (x = 0–1) ceramics were prepared through conventional solid-state method. This paper focused on the dependence of microwave dielectric properties on crystal structural characteristics via crystal structure refinement, Raman spectra study and complex chemical bond theory. XRD spectrums delineated the phase information of a spinel structure, and structural characteristic of these compositions were achieved with the help of Rietveld refinements. Raman spectrums were used to depict the correlations between vibrational phonon modes and dielectric properties. The variation of permittivity is ascribed to the Mg2(Ti1-xSnx)O4 average bond covalency. The relationship among the B-site octahedral bond energy, tetrahedral bond energy and temperature coefficient are discussed by defining on the change rate of bond energy and the contribution rate of octahedral bond energy. The quality factor is affected by systematic total lattice energy, and the research of XPS patterns illustrated that oxygen vacancies can be effectively restrained in rich oxygen sintering process. Obviously, the microwave dielectric properties of Mg2(Ti1-xSnx)O4 compounds were obtained ( e r = 12.18, Q × f = 170,130 GHz, τ f = −53.1 ppm/°C, x = 0.2).

Influence of NaNbO3 on the structural, optical and dielectric properties of 0.05(K0.5Bi0.5TiO3)–0.95(NaNbO3) composites ceramics

A new polycrystalline lead-free 0.05(K0.5Bi0.5TiO3)–0.95(NaNbO3) (KBT–NN) composites ceramics have been prepared by solid-state reaction method and their structural, optical, dielectric, ferroelectric and impedance properties are investigated. X-ray diffraction and Rietveld refinement data reveal that this composites ceramics possesses a perovskite-type orthorhombic structure after the diffusion of K0.5Bi0.5TiO3 into the NaNbO3. An appreciable change in its vibrational phonon modes of KBT on addition of NaNbO3 is exhibited in the material as observed from Fourier-transform infrared spectroscopy (FT-IR) spectrum. The optical band gap energy of the sample is determined from the diffused absorbance spectra to be 3.2 eV, which may be useful in photo-catalytic application. In the frequency range of 130–900 cm−1, different vibrational modes are observed from Raman spectrum. Field emission scanning electron microscopy (FE-SEM) images reveal a well-defined and homogeneous morphology. Polarization vs. electric field study confirms the ferroelectricity. Dielectric and complex impedance spectroscopic studies are performed over a wide range of frequency (i.e., 103–106 Hz) and temperature (30°–500 °C) and it is found that Jonscher’s power law is well applicable to the alternating current (ac) conductivity spectrum. The direct current (dc) conductivity of the material, which depends upon temperature, exhibits the decrease resistance with increase of temperature similar to that of semiconductors. The dc conductivity confirms that the conduction mechanism is influenced by oxygen vacancies.

Probing Interfacial Surface State Excitons in Nanoscale Synthesized CuxS/MoS2 Heterostructure

AbstractTwo dimensional (2D) layer integration of different materials facilitates new functionalities in material engineering to produce novel structures with specialized properties. Fabrication of large‐scale 2D heterostructure with atomically clean interface, and unveiling the distinct interlayer transition, is a challenging process. In this paper, the vertical heterostructure of copper sulfide (CuxS) and molybdenum disulfide (MoS2) nanosheets is synthesized by sulfurization of pre‐deposited metal films. Optical bandgap transition and phonon vibration frequency are observed in the heterojunction area with respect to individual nanosheets. Raman shift in phonon vibration modes of MoS2 shows the interlayer coupling effect. Photoluminescence (PL) intensity of monolayer MoS2 is quenched due to bandgap offset interlayer transition. Bandgap alignment of CuxS (1 < x < 2) with MoS2 is a tunable staggered symmetry that yields charge transfer at the heterostructure interface. Photoexcited electron–hole pairs are moving across the interface much faster than recombining into the intralayer excitons. The synthesized CuxS/MoS2 heterostructure is well defined over a large area, with controllable thickness and a scalable position. Heterostructure has great potential for future device applications in optoelectronics based on optical excitonic response and charge carrier dynamics.

Fluorinated Organic Electro‐Optic Quinolinium Crystals for THz Wave Generation

AbstractFluorinated electro‐optic crystals with state‐of‐the‐art second‐order nonlinear optical response and excellent characteristics for terahertz (THz) wave generation are reported. The fluorinated organic ionic crystals consist of optically highly nonlinear fluorinated HM6FQ (6‐fluoro‐2‐(4‐hydroxy‐3‐methoxystyryl)‐1‐methylquinolinium) or HM7FQ (7‐fluoro‐2‐(4‐hydroxy‐3‐methoxystyryl)‐1‐methylquinolinium) cations and 4‐methylbenzenesulfonate (T) counter anions. Compared to benchmark electro‐optic crystals based on nonfluorinated HMQ (2‐(4‐hydroxy‐3‐methoxystyryl)‐1‐methylquinolinium) cations, introducing fluorine substituent on HM6FQ cations creates additional hydrogen bonds (ArF···HC). Such a molecular engineering leads to an enhanced thermal stability and significant modulations of phonon vibrational modes of crystals in THz frequency region, while excellent π–π stacking and space filling characteristics of HM6FQ cations in crystals lead to state‐of‐the‐art diagonal component of the macroscopic nonlinear optical susceptibility, similar to the case of HMQ cations. HM6FQ‐based crystals exhibit a very high optical‐to‐THz conversion efficiency, comparable to benchmark HMQ‐based crystals. In addition, due to additional hydrogen bonds induced by fluorine substituents, the spectral shape of the generated THz wave is remarkably modified; e.g., the largest spectral gap is near 1.5 and 2.0 THz for HM6FQ‐ and HMQ‐based crystals, respectively. The fluorinated cationic engineering on nonlinear optical crystals having benchmark nonlinear optical response is, as far as is known, reported for the first time.

Raman spectroscopic, infrared spectra and microwave dielectric properties in the (ZrTi)1−x(Al1/2Nb1/2)2xO4 ceramics

A series of (ZrTi)1−x(Al1/2Nb1/2)2xO4 (0.12 ≤ x ≤ 0.30) ceramics with suitable sintering aids of 0.5 wt% CuO were successfully synthesized by the conventional solid-state processing. The XRD analysis suggested that the main crystalline phase of the well-densified ceramics belonged to α-PbO2-type structure. The SEM demonstrated that the appropriate sintering aids and the proper sintering temperature led to a densification of the ceramics by observing the microstructure. Raman spectroscopic and Far Infrared reflectivity spectra were applied to explore the relation between microwave dielectric properties and microstructure by learning the phonon vibrational modes. An excellent microwave dielectric properties (er ~ 36.5, Qf ~ 36200 GHz, τf ~ 0 ppm/°C) was achieved in (ZrTi)1−x(Al1/2Nb1/2)2xO4 ceramics sintered at 1350 °C for 4 h when x = 0.18. The results revealed this ceramic system is a very promising candidate for microwave dielectric applications requiring extremely near zero τf.

First-principles study of lattice dynamical and thermodynamic properties of Li<sub>2</sub>NH

<sec>One of the key issues for scale applications of hydrogen energy is the availability of safe, efficient and ecnomicical hydrogen storage technologies. In the past few years, light metal hydrides have attracted considerable attention due to their high hydrogen capacity. With a hydrogen capacity up to ~6.5 wt%, Li<sub>2</sub>NH is regarded as one of the most promising hydrogen storage materials. Although the hydrogen physical and thermodynamic properties of Li<sub>2</sub>NH have been studied, the electronic structure, phonon vibration mode and thermodynamic properties of Li<sub>2</sub>NH have not yet been resolved. In this paper, by using the first principles based on the density functional theory (DFT), we investigate the electronic structure, lattice dynamical and thermodynamic properties of Li<sub>2</sub>NH in detail.</sec><sec>Firstly, the structure of Li<sub>2</sub>NH is optimized and the lattice parameters and total energy of the crystals are calculated. As shown by the calculation results, the lattice parameters are in good agreement with previous theoretical and experimental results. Our lowest-energy structure of Li<sub>2</sub>NH has orthorhombic <i>Pnma</i> symmetry at <i>T</i>=0 K for all of the proposed structures. Secondly, the electronic band-structure studies reveal that Li<sub>2</sub>NH has a small band gap of about 2.0 eV. The analysis of total and partial density of states of Li<sub>2</sub>NH show that the bonding between the N and H has a covalent character. Thirdly, the lattice dynamical properties of Li<sub>2</sub>NH are investgated at the corresponding equilibrium states. These results show that only the phonon dispersion curves of Li<sub>2</sub>NH (<i>Pnma</i>) without negative frequencies are calculated along the high-symmetry points. The optical modes of phonon frequencies at <i>Γ</i> point are assigned as Raman and Infrared-active modes. Based on the calculated phonon density of states, the thermodynamic properties are computed, such as the Helmholtz free energy, internal energy, entropy and the constant-volume specific heat versus temperature. The calculation results may explore the applications in areas of hydrogen storage for Li-N-H, which is of great importance forusing hydrogen in the future.</sec>

First-principles study of the layered thermoelectric material TiNBr.

Layer-structured materials are often considered to be good candidates for thermoelectric materials, because they tend to exhibit intrinsically low thermal conductivity as a result of atomic interlayer interactions. The electrical properties of layer-structured materials can be easily tuned using various methods, such as band modification and intercalation. We report TiNBr, as a member of the layer-structured metal nitride halide system MNX (M = Ti, Zr, Hf; X = Cl, Br, I), and it exhibits an ultrahigh Seebeck coefficient of 2215 μV K−1 at 300 K. The value of the dimensionless figure of merit, ZT, along the A axis can be as high as 0.661 at 800 K, corresponding to a lattice thermal conductivity as low as 1.34 W (m K)−1. The low κl of TiNBr is associated with a collectively low phonon group velocity (2.05 × 103 m s−1 on average) and large phonon anharmonicity that can be quantified using the Grüneisen parameter and three-phonon processes. Animation of the atomic motion in highly anharmonic modes mainly involves the motion of N atoms, and the charge density difference reveals that the N atoms become polarized with the merging of anharmonicity. Moreover, the fitting procedure of the energy–displacement curve verifies that in addition to the three-phonon processes, the fourth-order anharmonic effect is also important in the integral anharmonicity of TiNBr. Our work is the first study of the thermoelectric properties of TiNBr and may help establish a connection between the low lattice thermal conductivity and the behavior of phonon vibrational modes.

Boron nitride nanochannels encapsulating a water/heavy water layer for energy applications.

Water interaction and transport through nanochannels of two-dimensional (2D) nanomaterials hold great promises in several applications including separation, energy harvesting and drug delivery. However, the fundamental underpinning of the electronic phenomena at the interface of such systems is poorly understood. Inspired by recent experiments, herein, we focus on water/heavy water in boron nitride (BN) nanochannels – as a model system – and report a series of ab initio based density functional theory (DFT) calculations on correlating the stability of adsorption and interfacial properties, decoding various synergies in the complex interfacial interactions of water encapsulated in BN nanocapillaries. We provide a comparison of phonon vibrational modes of water and heavy water (D2O) captured in bilayer BN (BLBN) to compare their mobility and group speed as a key factor for separation mechanisms. This finding, combined with the fundamental insights into the nature of the interfacial properties, provides key hypotheses for the design of nanochannels.

Anisotropic Electron-Phonon Interactions in Angle-Resolved Raman Study of Strained Black Phosphorus.

Few-layer black phosphorus (BP) with an in-plane puckered crystalline structure has attracted intense interest for strain engineering due to both its significant anisotropy in mechanical and electrical properties and its high intrinsic strain limit. Here, we investigated the phonon response of few layer BP under uniaxial tensile strain (∼7%) with in situ polarized Raman spectroscopy. Together with the first-principles density functional theory (DFT) analysis, the anisotropic Poisson's ratio in few-layer BP was verified as one of the primary factors that caused the large discrepancy in the trend of reported Raman frequency shift for strained BP, armchair (AC) direction in particular. By carefully including and excluding the anisotropic Poisson's ratio in the DFT emulations, we rebuilt both trends reported for Raman mode shifts. Furthermore, the angle-resolved Raman spectroscopy was conducted in situ under tensile strain for systematic investigation of the in-plane anisotropy of BP phonon response. The experimentally observed thickness and crystallographic orientation dependence is elaborated using DFT theory as having a strong correlation between the strain-perturbated electronic-band structure and the phonon vibration modes. This study provides insight, both experimentally and theoretically, for the complex electron-phonon interaction behavior in strained BP, which enables diverse possibilities for the strain engineering of electrical and optical properties in BP and similar two-dimensional nanomaterials.

Absence of ferromagnetism in ferroelectric Mn‐doped BaTiO3 nanofibers

AbstractPure and Mn‐doped barium titanate nanofibers were synthesized by the electrospinning method. The morphology, microstructure and crystal structure of as‐spun and annealed composite nanofibers were characterized by scanning electron microscopy and transmission electron microscopy. After annealing at 850°C, we obtain nanofibers a few μm long, formed by nanoparticles of irregular shape with sizes around 100 nm. X‐ray diffraction and Raman spectroscopy show that a partial phase transition from tetragonal to hexagonal takes place for BaTi0.90Mn0.10O3. Vibrational phonon modes were calculated for BaTiO3 within the density functional theory (DFT) framework. Ferroelectricity has been probed on pure and Mn‐doped BaTiO3 nanofibers, by means of piezoresponse force microscopy in an atomic force microscope, confirming the polar domain switching behavior of the fibers. The measured piezoelectric coefficient d33 were 31 and 22 pm/V for BaTiO3 and BaTi0.90Mn0.10O3. Magnetic properties of the samples were probed in a superconducting quantum interference device. Diamagnetic and paramagnetic behaviors were found in pure and Mn‐doped samples, respectively.

Euphorbia heterophylla (L.) mediated fabrication of ZnO NPs: Characterization and evaluation of antibacterial and anticancer properties

Abstract Euphorbia heterophylla leaves extract mediated synthesis of multifunctional Zinc oxide nanoparticles (ZnO NPs) by green chemistry approaches. The prepared product was well characterized using various analytical tools namely X-ray diffraction (XRD), Ultra Violet-Diffused reflectance spectroscopy (UV-DRS), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, Scanning electron microscopy (SEM), Energy dispersive X-ray analysis (EDAX) and Transmission electron microscopy (TEM) etc. The XRD pattern of ZnO NPs showed hexagonal phase with wurtzite structure. The UV-DR Spectrum reveled that characteristic peak at 370 nm and its energy band gap was found to be ~3.15 eV indicating the formation of ZnO NPs. The FT-IR spectrum results showed the presence of functional groups. The Raman spectrum showed the presence of phonon modes of vibrations in ZnO NPs. The morphological analysis of ZnO NPs exhibit hexagonal, conical and pyramidal nature with mean particle size of ~40 nm which is in close agreement with XRD pattern. ZnO NPs shows significant antibacterial activity against pathogenic bacterial strains both Gram positive and Gram negative bacteria by agar well diffusion method. Furthermore, the cytotoxicity of ZnO NPs was evaluated against cancer cell lines such as lung (A549) and hepatocellular carcinoma (HepG2) cell lines. Therefore, the study reveals that, the E. heterophylla is an effective reducing agent for the formation of ZnO NPs with significant antibacterial and cytotoxicity properties.

Sn doped α-Fe2O3 (Sn=0,10,20,30 wt%) photoanodes for photoelectrochemical water splitting applications

Abstract One pot hydrothermal route was adapted to synthesis pristine and Sn doped α-Fe2O3 nanospheres successfully. Sharp high intense diffraction peaks obtained from XRD confirmed crystalline nature of rhombohedral hematite. The secondary SnO2 face formation was due to increasing Sn dopant concentration. Raman spectra confirmed intrinsic phonon vibration modes [Eg(1)+Eg(2)+Eu] of hematite nanospheres. 2P3/2(1) → 2P1/2 transition by emission peak at 549 nm confirmed hematite phase formation. Metal oxygen vibration (Fe O stretching) was confirmed by absorption band situated at 539 cm−1. The noticeable variation in band gap of pristine hematite nanospheres was due to tetravalent Sn4+ dopant concentration. The lowest band gap energy 1.90 eV was found for 10 wt% Sn4+ doped hematite. Highest photocurrent 2.34 mA/cm2 at 0.098 V V RHE was obtained for 10% Sn doped hematite nanospheres. The EIS exposed the charge transferring mechanism of synthesized pristine and Sn doped α-Fe2O3 nanospheres. M-S plot evidenced that the lower shift of flat band potential for 10 wt% Sn4+ doped hematite was as −0.35 V. CA study proved the good stability over 4 h of the best performed photoanodes. Sn4+ doping and its dopant concentration on pristine hematite had dominant effect on photocatalytic activity of hematite nanospheres.

First-Principles Study of Water Nanotubes Captured Inside Carbon/Boron Nitride Nanotubes.

Water confined to nanopores such as carbon nanotubes (CNTs) exhibits different states, enabling the study of solidlike water nanotubes (WNTs) and the potential application of their properties due to confined effects. Herein, we report the interfacial interaction and particular stabilized boundaries of confined WNTs within CNTs and boron nitride nanotubes (BNNTs) using first-principles calculations. We demonstrate that the intermolecular potential of nanotube walls exerts diameter-dependent additive or subtractive van der Waals (vdW) pressure on the WNTs, altering the phase boundaries. Our results reveal that the most stable WNT@CNT is associated with a CNT diameter of 10.5 Å. By correlating the stability of WNTs with interfacial properties such as the vdW pressure and vibrational phonon modes of confined WNTs, we decode and compare various synergies in water interaction and stabilized states within the CNTs and BNNTs, including interfacial properties of WNT@BNNTs that are more significant than those of WNT@CNTs. Our results suggest that the transition of a water tube to an ice tube is strongly dependent on the diameter of the confining CNT or BNNT, providing new insights on leveraging the interfacial interaction mechanism of confined WNTs and their potential application for fabricating nanochannels and nanocapacitors.

Exploring Multifunctional Applications of Hexagonal Boron Arsenide Sheet: A DFT Study

The electronic, transport, optical, thermoelectric, and thermodynamic properties of the two-dimensional (2D) stable monolayer of boron arsenide (BAs) sheets have been investigated using state-of-art theoretical calculations. The energetic, dynamic, thermal, and mechanical stability of the BAs sheet have also been studied to unravel the feasibility of experimental realization of this material. Interestingly, the band gap of this semiconducting sheet changes from direct into indirect band gap material by the application of biaxial strain of 10% and it becomes metallic at 14% of biaxial strain. Furthermore, positive phonon vibrational modes have been observed for all applied biaxial strains, which ensure the stability of the sheet under strain. The semiconducting property is preserved when cutting 2D sheet into one-dimensional nanoribbons, and the band gap is size dependent. In addition, the calculated optical properties exhibit strong anisotropy. BAs nanomaterial has strong adsorption in the UV–visible region. The calculated Seebeck coefficient and power factor values show that BAs sheet is an ideal candidate for thermal management and thermoelectric applications. Finally, the thermodynamic properties have been calculated on the basis of the phonon frequencies. These rich properties of BAs nanosheets endow the system with promising applications in nanoelectronics and photovoltaics.

Pure and cobalt-substituted zinc-ferrite magnetic ceramics for supercapacitor applications

Pure and cobalt-substituted zinc ferrites were successfully synthesized employing a simple co-precipitation route. CoxZn0.04−xFe2O4 (x = 0, 0.01, 0.02) physical properties have been investigated employing comprehensive characterization studies. XRD results confirmed the cobalt substitution in zinc-ferrite magnetic ceramics. SEM analysis revealed non-uniform cluster formation with large agglomeration and more number of spherical grain nanoparticles in the range of 30–150 nm. Raman phonon vibration modes [F2g(1) + F2g(2) + A1g] revealed cubic zinc-ferrite phase and cobalt substitution. Product-predominant blue–green emission was observed in PL studies. IR results confirmed ferrite tetrahedral (~ 540–565cm−1) and octahedral sites’ (~ 428 cm−1) metal oxygen vibrations. Electrochemical studies confirmed an appreciable increase in specific capacitance of Co0.02Zn0.02Fe2O4 around 377 F/g at 10 mV/s scan rate. Cobalt substitution in zinc spinel ferrite structure revealed dominant influence on structural, optical, and electrochemical properties of the obtained product.

Electro/mechanical mutable properties of black phosphorene by electric field and strain engineering

Phosphorene a two dimensional (2D) arrangement of black phosphorus atoms has greatly manifested extraordinary properties. In this work we investigated the electronic and mechanical properties of a deformed structural (i.e. modified two characteristic angles) single-layer black phosphorus using tight-binding (TB) Hamiltonian and Green’s function approach, where a planar and a most puckered structure have been created by modifying the angle between two nearest neighboring P–P bond from two sublayers. Moreover, by using density functional theory (DFT), we show that the applied strain in the x, y axes and electric field can be used to tune the electronic properties of black phosphorene. We also provide a comparison of phonon vibrational modes of planar and puckered phosphorene to compare their structure stability. It was found that by structural deformation such as modifying the angle between two nearest neighboring P–P bond from two sublayers, consequently having a planar and a most puckered structure, no change can be seen for the effective masses along the y (zigzag) direction, but totally affected along the x (armchair) direction leading to heavier electrons and holes. Furthermore, 2D phosphorene exhibits different stiffness for applied strain in the x, y direction. Such rich variety of electronic, mechanical and structural transformations provides 2D phosphorene as a unique material for fundamental physics studies and applicable in nanoelectronic and nanophotonics devices.

Electrical and optical properties of lead-free 0.15(K0.5Bi0.5TiO3)–0.85(NaNbO3) solid solution

Polycrystalline lead free 0.15(K0.5Bi0.5TiO3)–0.85(NaNbO3) ceramic is synthesized using conventional solid state reaction technique. Structural, dielectric, optical and impedance properties of the sample are investigated. X-ray diffraction (XRD) study reveals K0.5B0.5TiO3 (KBT) diffusing into the NaNbO3 (NN) lattices to form a new perovskite-type solid solution with orthorhombic structure (space group Pmc2 1 ) at room temperature. Addition of small amount of KBT transforms NN ceramic from anti-ferroelectric to ferroelectric material. The XRD data has been refined using Rietveld refinement technique. FTIR spectra reflect an appreciable change in its vibrational phonon modes of the sample. The optical band gap is estimated to be 3.02 eV from the diffused absorbance spectra, which is useful in photo catalytic applications. Different vibrational modes in the frequency range of 130–900 cm−1 is observed from the Raman spectrum. FESEM micrograph reveals the homogeneous grains and well-defined grain boundaries with some few pores. Dielectric and complex impedance spectroscopic studies are carried out in a wide range of frequency (i.e., 103–106 Hz) and temperature (30–475 °C). The presence of ferroelectric properties is confirmed from P–E loop. A strong correlation between its microstructure and electrical parameters is established from the study of the electrical properties of the material. The ac conductivity spectrum obeys Jonscher’s power law. Negative temperature coefficient of resistance behavior of the material is inferred from temperature dependence of dc conductivity.

Spontaneous, high temperature and spectroscopic characterization of K0.5Bi0.5TiO3-NaVO3 ceramic

Ferroelectric, optical and impedance properties of polycrystalline K0.5Bi0.5TiO3-NaVO3 (KBT-NV) ceramic prepared by solid state reaction technique has been investigated. Field Emission Scanning Electron Microscope (FESEM) study of the gold coated sintered pellet of the sample exhibits uniform distribution of small grains with well-defined grain boundaries. The Fourier Transform Infrared (FTIR) spectra show that the compound exhibits an appreciable change in its vibrational phonon modes of KBT on addition of NaVO3. The X-ray diffraction (XRD) reveals an orthorhombic structure where the crystallites preferentially grows along (6 2 0) face. Studies on nature of polarization, variation of dielectric constant, and tangent loss with temperature as well as frequency indicate the possible existence of ferroelectricity. The temperature variation of hysteresis loop confirms the ferroelectric nature in the studied compound. The sample is found to be photoluminescent in the wavelength range of 540–570 nm with a strong greenish-red emission which originates from defects. The optical band gap of the KBT-NV sample has been estimated from diffused reflectance and absorbance spectra to be 2.68 eV, which can be useful for photocatalytic application.