Growth and characterization of l-histidine cadmium chloride monohydrate a semiorganic nonlinear optical crystals

l-histidine cadmium chloride monohydrate (LHCCM), a semiorganic nonlinear optical material was grown from aqueous solution by slow solvent evaporation method at room temperature. The LHCCM crystals were characterized by X-ray powder diffraction analysis. The presence of functional groups was identified through fourier transform infrared spectroscopy. Thermogravimetric and differential thermal analysis confirms that the crystal is stable up to 277 °C. The dielectric constant was studied as a function of frequency for various temperatures. The mechanical properties of the grown crystals have been studied using Vickers microhardness tester. The second harmonic generation behavior of LHCCM crystal was tested by modified Kurtz–Perry powder technique.     

Acoustic anomalies and relaxation dynamics of relaxor ferroelectric Na1/2Bi1/2TiO3 single crystals studied by using Brillouin spectroscopy

Acoustic anomalies of relaxor ferroelectric Na_1/2Bi_1/2TiO₃ single crystals were investigated over a wide temperature range from −196 °C to 900 °C by using Brillouin spectroscopy. The longitudinal sound velocity, the acoustic absorption coefficient and the elastic constant C₁₁ were determined for the acoustic phonon mode propagating in the [100] direction. Two acoustic anomalies, weaker ones at the cubic-tetragonal phase transition temperature of ~540 °C and more pronounced ones at temperatures near 315 °C near the dielectric maximum temperature, were investigated and discussed in relation with the relevant order parameters coupled to the acoustic waves. The relaxation dynamics in the cubic phase were studied based on the flattening of the mode frequency and the half width, which was observed for the first time, and a modified Arrhenius law.     

Improved dielectric and AC conductivity properties of P(VDF-TrFE)-Nafion blends for high-temperature flexible capacitor applications

The free-standing poly (vinylidene fluoride-trifluoroethylene) [P(VDF-TrFe)] and P(VDF-TrFe)-Nafion blended films were fabricated using the casting method. The XRD and FTIR confirmed the electro-active β-phase of P(VDF-TrFe). The morphological changes were studied through SEM analysis of the blends. The dielectric and ac conductivity measurements were carried out as a function of temperature from 30 °C to 130 °C in the frequency range of 100 Hz - 1 MHz. The dielectric constant reveled a ferroelectric to paraelectric transition in all the samples with a decrease in the transition temperature of the blends. The temperature-dependent ac conductivity and power law analysis demonstrated the presence of a correlated barrier hoping mechanism with a change in the motional behavior in the blends. The blended films exhibited low dielectric loss and more stable dielecric properties with temperature in comparison to P(VDF-TrFe). These films demonstrated the potential to be used in high-temperature flexible capacitor applications.     

Mechanism of the polarization response in the relaxor state of lead scandotantalate single crystals with different levels of ion ordering

The dielectric properties and optical transmission of stoichiometric lead scandotantalate (PST) single crystals in strong electric fields was studied above the temperature of the spontaneous ferroelectric phase transition (T_sp). It is shown that the mechanism of polarization response directly above T_sp is related to induced polarization effects and macrohysteretic behavior only in ac fields above 5 kV/cm. Ananalysis of reciprocal dielectric permittivity carried out over a broad temperature range far above the temperature at which the dielectric permittivity passes through a maximum revealed that specific features of the relaxor behavior manifest themselves up to 400°C even in highly ordered PST crystals.     

Pyroelectric coefficient manipulation in doped TGS crystals

Pure and l-alanine doped Triglycine sulphate (TGS) crystals were grown in paraelectric phase (∼52 °C). Doped crystals show unequal growth rates along the ferroelectric axis. Pure TGS crystals show peculiar dielectric behavior in the ferroelectric phase, after crossing up and down the Curie point in two successive runs between room temperature and 80 °C. Much higher and unstable permittivity was found returning in the ferroelectric phase. At constant temperature (35 °C), permittivity follows a relaxation process, characterized by two relaxation times. l-Alanine doped TGS crystal shows more than one order of magnitude smaller permittivity and dielectric losses. Internal bias field of ∼1 kV/cm, induced by the dopant, made the crystal almost monodomain and pined polarization in one direction. Pyroelectric coefficient measurements were performed at constant heating rate of the samples, using a computer controlled He cryostat and Keithley 6517 electrometer. The temperature dependence of P⁺ polarization component, obtained by computer integration of the pyroelectric coefficient, was measured on a large temperature interval (−20/+80 °C). Pyroelectric coefficient of the doped samples was also measured by the same procedure, using a dc bias electric field, pointing in the opposite direction to the pined polarization. The polarization could be reversed, on the whole temperature range, by dc fields higher than bias or coercive field. Surprisingly, for the first time, the pyroelectric coefficient (p) was found constant on quite large temperature intervals. Doped TGS crystals show much smaller values of permittivity ?_r versus the pure one and consequently, get higher figure of merit M = p/?_r. The pyroelectric coefficient of this material can be tailored to become constant on a defined temperature range, under a dc field control. This characteristic makes this material valuable to be used as pyroelectric material for IR devices.     

Dielectric characteristics and thermal behaviour of terbium fumarate heptahydrate crystals

Dielectric properties, ac conductivity and thermal characteristics of terbium fumarate heptahydrate crystals grown by gel diffusion method have been carried out. The real part of dielectric constant, dielectric loss and ac conductivity of the material have been measured as a function of temperature and frequency of the applied electric field. Dielectric constant, dielectric loss and ac conductivity of the title compound were systematically investigated, showing a hump at about 85 °C, which could be attributed to water molecules in the crystal boundary. The dielectric anomaly exhibited by the material has been correlated with its thermal behaviour. The ac conductivity of the material obeys the Jonscher's power law relation; σ(ω) = σ_o + Aω^s, with the temperature dependent power exponent s < 1. The ac conductivity of the compound has been found to increase with the increase in frequency. The material is suggested to show protonic conduction. The non-isothermal kinetics was used to evaluate the activation energy for the dehydration step of thermal decomposition of terbium fumarate heptahydrate by using the Coats–Redfern integral method.     

Evidence of sustained ferroelectricity in glycine sodium nitrate single crystal

The nonlinear optical single crystals of glycine sodium nitrate were grown by the slow evaporation method. XRD confirmed monoclinic structure. Thermal stability and melting point (225 °C) were investigated. The dielectric behaviour of the crystals in the frequency range 20 Hz–2 MHz at different temperatures is reported in which a ferroelectric to paraelectric phase transition at T_c = 56 °C is observed. The activation energies of GSN were found to be 3.615 eV, 0.593 eV and 0.0733 eV in three temperature regions of conductivity plot due to a hopping conduction mechanism. The crystal has shown high piezoelectric charge coefficient (d₃₃) of 16 pC/N which is nearly double of observed value for γ-glycine single crystal. The spontaneous polarization P_s at room temperature was found to be 1.489 μC/cm² at applied maximum field of 26 kV/cm (1.194 μC/cm² at 12 kV/cm) and the pyroelectric coefficient was determined to be 400 μC/m²/°C. High value of squareness parameter (1.93) makes the GSN crystal suitable for switching applications. Detailed investigations of Ferro-/Piezoelectricity were observed for the first time in glycine sodium nitrate crystals which was found to preserve the ferroelectricity even after applying an electric field much higher than the saturation electric field (12–26 kV/cm). Application of GSN crystals as sensor, high power switch gears and storage memories has been established.     

Growth and characterization of semi organic nonlinear optical l-Valine Ferric Chloride single crystal by solution growth technique

l-Valine Ferric Chloride single crystal is a new semi organic nonlinear optical material. It has been grown from a mixture of aqueous solutions of l-Valine and Ferric Chloride by slow evaporation solution growth technique at room temperature for the first time. Single crystal XRD analysis revealed that the crystal system belongs to Cubic P with cell parameters are a = 24.38 Å, b = 24.38 Å, c = 24.38 Å and volume is 14,485 Å³. The UV spectrum shows existence of wide transparency window suitable for optoelectronic applications. Thermal stability and melting temperature of the as grown crystal was identified from TG-DTA analysis. Spectroscopic studies have been carried out for analyzing the presence of functional groups, thermal stability and phase transition of the grown crystal. The dielectric loss and the dielectric constant of the crystals were measured as a function of frequency. Photoluminescence study was carried out for grown crystals and the maximum emission occurs has good optical transmission in the entire visible region. Second harmonic generation (SHG) conversion efficiency has been estimated.     

Domain,dielectric and optical studies in antiferroelectric (Pb,La) (Zr,Sn, Ti)O3 single crystals

Antiferroelectric (Pb, La) (Zr, Sn, Ti)O₃ (PLZST) single crystals have been successfully grown by flux method using PbO–PbF₂–B₂O₃ as the flux. The obtained crystals are pale yellow in color and translucent. Domain structures, dielectric constants and optical transmission measurements have been performed on the 〈001〉-oriented PLZST single crystals. Two types of domains, namely, 90° and 180° domains, are observed. The extinction of 90° domains at P/A: 0° reveals a tetragonal structure in the crystal. The sequence of phase transitions from antiferroelectric to ferroelectric and then paraelectric has been established with increasing temperature. According to the modified Curie–Weiss relationship, the PLZST crystal is in an intermediate state between normal and relaxor antiferroelectrics. The broad optical transparent region (from 0.4 to 7.0 μm) and high optical transmittance (up to 65%) indicate that PLZST crystals are promising for optical uses.     

Enhanced properties of cadmium mercury thiocyanate bis(N-methyl formamide): A promising non-linear optical crystal

The present study deals with the synthesis and characterization of cadmium mercury thiocyanate bis(N-methyl formamide) or CMTN crystals where they were grown in two critical steps. In the first step, cadmium mercury thiocyanate (CMTC) single crystals were grown by intriguing cadmium chloride, mercuric chloride, and ammonium thiocyanate in 1:1:4 ratio and mixed with solvent by a slow solvent evaporation technique. The second step involves the reaction between CMTC and N-methyl formamide (NMF) in a 1:2 ratio leading to the formation of CMTN crystals. The growth parameters of CMTN grown crystals were optimized at different pHs (1- 5) and the solubility curve has also been reported. On characterization, the orthorhombic crystallinity having Pna2₁ space group of as-grown CMTN crystals has been revealed by single X-ray diffraction analysis (XRD) and the lattice cell parameters are found to be a = 15.195 Å, b =  7.722Å, c = 16.162 Å, and α = β = γ = 90°. Single the phase crystallinity of CMTN is observed by powder XRD pattern and the increase in the intensity of index peaks shows that there exists good coordination between the CMTC and NMF compounds. The FTIR analysis supported the presence of surface ligands groups of thiocyanate, while the Raman spectroscopy confirmed for the coordination of thiocyanate ions in the CMTN compound and thus both established for the metal-ligand bonding. The UV-vis spectroscopy showed the optical transparency of CMTN to have the cutoff wavelength at 335 nm and the Kurtz powder method for studying the second harmonic generation (SHG) output power is 5 times higher than the reference. Further increase of dielectric constant and dielectric loss with respect to the changes in frequency makes it a suitable material for the construction of photonic and non-linear optical (NLO) devices.     

Dielectric properties of deuterated ammonium Rochelle salt

The dielectric constant of deuterated ammonium Rochelle salt along the three crystallographic axes as well as the pyroelectric charge density developed on the crystal surface perpendicularly to the b-axis have been measured with a high temperature resolution. The para- to ferroelectric transition at T_c = ?159°C shows a thermal hysteresis of ΔT = 0.15°C. This and the discontinuities in the dielectric constant along all three axes show that the phase transition is of the first-order. No phase intermediate between the para- and the ferroelectric phases could be detected.     

Preparation of fine-grain lead indium niobate ceramics with wolframite precursor method and resulting electrical properties

In this study, lead indium niobate (Pb(In_1/2Nb_1/2)O₃ or PIN) ceramics were prepared by a wolframite precursor method via a vibro-milling technique. Fine-grain ceramics were achieved with average grain size of 1–2 μm, indicating advantage of the vibro-milling technique used. The dielectric and ferroelectric properties were measured by means of an automated dielectric measurement set-up and a standardized ferroelectric tester, respectively. The dielectric properties of PIN ceramic were measured as functions of both temperature and frequency. The results indicated that the dielectric properties of the PIN ceramic were of relaxor ferroelectric behavior with temperature of dielectric maximum (T_m)∼53 °C and dielectric constant (ε_r)∼4300 (at 1 kHz). The P–E hysteresis loop measurements at various temperatures showed that the ferroelectric properties of the PIN ceramic changed from the paraelectric behavior at temperature above T_m to slim-loop type relaxor behavior at temperature slightly below T_m. Moreover, the P–E loop became more open at temperatures much lower than T_m. PACS 77.22.Ch; 77.84.Dy     

Temperature dependent polariton measurements in BaTiO3

Polariton techniques are used to determine the temperature dependence of all three A₁ modes between room temperature and T_c = 134°C in the ferroelectric phase of BaTiO₃. The results shows that there is a large difference between the clamped dielectric constant, ?(0), determined from these results and ?(0) determined from microwave capacitance techniques. It is argued that, while soft modes in displacive ferroelectrics are the driving force for the transition, other oscillators play an important role in low frequency dielectric behavior.     

On the low temperature phase transition in (NH4)2SO4

An ultracryostat and multidecameter were used to determine the temperature dependence of the dielectric constant ?′ and dielectric loss ?″ over a wide range of frequencies of single crystals and polycrystalline samples of (NH₄)₂SO₄ in the region of the low temperature phase transition. A sharp increase was observed in the values of ?′ and ?″ at about ?50°C. In addition, a dielectric dispersion was detected and found to be more pronounced in the high temperature phase. This dispersion was attributed to piezoelectric resonance. The observed sudden increase in the values of the dielectric constant and dielectric loss below ? 50°C was attributed to the ferroelectric nature of the low temperature phase of (NH₄)₂SO₄.A DTA thermogram showed a sharp peak at ? 50°C which indicated that the phase transition is one of first order type. A TMA thermogram showed that this transformation was associated with a rapid increase in the expansion coefficient. Such an increase in the lattice parameter might be attributed to the enhanced rotation of electric dipoles associated with the distorted NH₄⁺ and SO₄^2? ions. The distortion of both the ammonium and sulfate ions in addition to their expected orientational motion are suggested to be responsible for the ferroelectric behaviour of ammonium sulfate below ?50°C.A transition to a metastable hexagonal state at about ?40°C is thought to occur, and this transformation is found to be irreversible.     

Effect of Al-doping on optical and electrical properties of spray pyrolytic nano-crystalline CdO thin films

CdO and Al-doped CdO nano-crystalline thin films have been prepared on glass at 300 °C substrate temperature by spray pyrolysis. The films are highly crystalline with grain size (18–32 nm) and found to be cubic structure with lattice constant averaged to 0.46877 nm. Al-doping increased the optical transmission of the film substantially. Direct band gap energy of CdO is 2.49 eV which decreased with increasing Al-doping. The refractive index and dielectric constant varies with photon energy and concentration of Al as well. The conductivity of un-doped CdO film shows metallic behavior at lower temperature region. This behavior dies out completely with doping of Al and exhibits semiconducting behavior for whole measured temperature range. Un-doped and Al-doped CdO is an n-type semiconductor having carrier concentration is of the order of ∼10²¹ cm⁻³, confirmed by Hall voltage and thermo-power measurements.     

Structural refinement,optical and ferroelectric properties of microcrystalline Ba(Zr0.05Ti0.95)O3 perovskite

For this study, a microcrystalline Ba(Zr_0.05Ti_0.95)O₃ (BZT) powder was prepared by a high energy ball milling method followed by calcination at 1100 °C for 4 h. The calcined powder was structurally characterized by X-ray diffraction and Rietveld refinement data, which showed that this material has a perovskite-type tetragonal structure with a space group of (P4mmm). The micro-Raman spectrum revealed local lattice distortions due to distorted octahedral [TiO₆] clusters. The temperature and frequency-dependent dielectric study of the BZT ceramic showed normal phase transition behavior. The ferroelectric property was studied by a P–E hysteresis loop. Optical band gap was investigated by ultraviolet–visible (UV–vis) absorption spectroscopy at room temperature. The UV–vis spectrum indicated that the BZT powder has an optical band gap of 3.15 eV.     

Impedance spectroscopy and dielectric analysis in KH2PO4 single crystal

Optical observation, differential scanning calorimetry, thermogravimetric analysis, and differential thermogravimetric measurements have been carried out on KH₂PO₄ single crystals. As compared with the optical observation of crystal under polarizing microscope, the dehydration process occurred gradually over the crystal surface at temperatures above 195 °C and then the interior of the sample. The ac impedance measurements were performed as a function of both frequency and temperature. The electrical conduction and dielectric relaxation have been studied. The activation energy of migration is 1.02 eV in the temperature range between 150 and 179 °C. The conduction mechanism in this temperature range is attributed to the hopping of proton among hydrogen vacancies. At temperatures above 186 °C, a higher conductivity activation energy with 2.94 eV is obtained. In addition to the proton conduction, the migration of the heavier ions (such as potassium ion) is also suggested.     

Influence of annealing temperature on optical properties of zinc oxide thin films analyzed by spectroscopic ellipsometry method

Zinc oxide (ZnO) thin films were sol–gel spin coated on glass substrates, annealed at various temperatures 300 °C, 400 °C and 500 °C and characterized by spectroscopic ellipsometry method. The optical properties of the films such as transmittance, refractive index, extinction coefficient, dielectric constant and optical band gap energy were determined from ellipsometric data recorded over the spectral range of 300–800 nm. The effect of annealing temperature in air on optical properties of the sol–gel derived ZnO thin films was studied. The transmission values of the annealed films were about 65% within the visible range. The optical band gap of the ZnO thin films were measured between 3.25 eV and 3.45 eV. Also the dispersion parameters such as single oscillator energy and dispersive energy were determined from the transmittance graph using the Wemple and DiDomenico model.     

A new ferroelectric oxide Li2Pb2Pr2W2Ti4Nb4O30: Synthesis and characterization

A new ferroelectric oxide (Li₂Pb₂Pr₂W₂Ti₄Nb₄O₃₀) of tungsten bronze structural family has been synthesized by a solid-state reaction (mixed-oxide) route at high temperature (～1100 °C). X-ray structural analysis with room temperature diffraction data confirms the formation of a single phase compound. The scanning electron microscopic (SEM) texture of the surface of material sample exhibits a uniform grain distribution with a few small voids suggesting the formation of high-density pellet sample. Detailed studies of dielectric constant, tangent loss and polarization with temperature and frequency confirmed the existence of ferroelectric properties in the material with transition temperature much above room temperature. Study of electrical properties (impedance, modulus, conductivity, etc.) of the material exhibits a strong correlation between its micro-structure (i.e., bulk, grain boundary, etc.) and electrical parameters. The nature of variation of dc conductivity with temperature confirms the Arrhenius behavior of the material. The presence of ionic conductivity in the material was observed in its ac conductivity spectrum. Study of frequency dependence of ac conductivity suggests that the material obeys Jonscher's universal power law. The experimental electrical transport properties of the material clearly exhibit the existence of non-exponential-type of conductivity relaxation.     

Growth,characterization and upconversion properties of erbium-doped potassium lithium tantalate niobate single crystals under 975 nm laser excitation

Potassium lithium tantalate niobate single crystals doped with erbium ions are grown by top-seeded solution growth method. The crystals are characterized by X-ray diffraction and differential thermal analysis. The refractive indices of the crystal are measured using ellipsometry method and fitted by Sellmeier equation. The as-grown crystals are tetragonal phase tungsten bronze-type structure with Curie temperature of 271.3 °C. Characteristic Er^3 + absorption bands are observed from 350 to 1100 nm in ultraviolet–visible-near infrared absorption spectra. These crystals emit brightly green and red upconversion fluorescence under 975 nm LD laser excitation, and the steady state upconversion spectra are obtained at room temperature. The red emission intensity increases as the erbium ions concentration increases in crystals. Processes of excited state absorption and energy transfer are responsible for upconversion luminescence. The emission intensities are quadratic dependences on pump power from pump power dependence analyses and deduction of transition rate equation model.