Synthesis and characterization of ferroelectric magnesium hydrogen phosphate single crystals

Ferroelectric Magnesium Hydrogen Phosphate MgHPO₄ (MHP) single crystals are grown by slow diffusion of magnesium chloride in sodium metasilicate gels impregnated with orthophosphoric acid. Bright and transparent prismatic, tabular, and isometric habit MHP crystals upto 3 × 2 × 1 mm³ are obtained. Results of chemical, X-ray diffraction, EDAX, microhardness and magnetic analysis are reported. The average etch pit density is determined by chemical etching to be 7 × 10³ cm⁻². Microtopographic investigations revealed the mechanism of crystal growth.     

Dielectric properties of ferroelectric lead hydrogen phosphate single crystals

The ferroelectric lead hydrogen phosphate (LHP) single crystals have been grown by employing the gel technique. The controlled reaction between lead nitrate and orthophosphoric acid solutions by diffusion process in gel medium has been used. The dielectric constant (ϵ′) and the dielectric loss (ϵ″) have been measured for the first time as a function of frequency in the range 10² to 10⁴ Hz. They have also been determined as a function of temperatures in the range 300 to 680 K. The polarisation effect contributing to the dielectric constant has been studied. It has been observed that the mechanism of the dielectric behaviour is different in the lower and higher temperatur and frequency ranges. The activation energy of the oscillators has been calculated and found to be 1.12 eV. Attempt has been made to draw some qualitative conclusions, taking in view, the existing theories of various kinds of polarization and implications have been discussed.     

Electrical conduction in ferroelectric lead hydrogen phosphate single crystals

Single crystals of LHP (Lead Hydrogen Phosphate) have been grown using the controlled reaction between lead nitrate and orthophosphoric acid solution by diffusion process in silica gel medium. Transparent crystals upto 6 × 4 × 3 mm³ in size have been grown at room temperature. The d.c. electrical conductivity of both single crystals and pelletized samples of LHP have been studied in the temperature range from 313 to 968 K. It has been observed that: (i) the d.c. conductivity of the crystalline sample is greater than that of thepellet sample, (ii) three distinct electrical conductivity processes have been observed and are interpreted as extrinsic, intrinsic, phase changes, and (iii) the activation energy for the conduction in the crystalline sample is greater than that of the pellet sample. The magnetic susceptibility measurements reveal that the paramagnetic characteristic of these materials and the implications are discussed.     

Domain structure and dielectric properties of TGS and DTGS single crystals depending on growth conditions

The influence of growth temperature and supersaturation of solution on domain structure and dielectric properties of TGS and DTGS single crystals was investigated. The qualitative and quantitative analysis of domain structures was carried out. The optimal growth conditions were found. It proves to be useful to arrange the measured values in table where lines correspond to growth temperatures and columns – to supersaturations for investigation of optimal growth conditions. The diagonal of extremal values exists in this table. The existence of optimal growth conditions explains in terms of interaction between domain and defect structures.     

Electrical conductivity and dielectric properties of potassium sulfamate single crystals

Single crystals of potassium sulfamate are grown by the method of slow evaporation at constant temperature. AC electrical conductivity of potassium sulfamate is measured in the temperature range 300–430 K and in the frequency region between 100 Hz and 3 MHz along the a, b and c‐axes. Complex impedance spectroscopy is used to investigate the frequency response of the electrical properties of the potassium sulfamate single crystal. Temperature variation of AC conductivity and dielectric measurements show a slope change around 345 K for both heating and cooling run and this anomaly is attributed as phase transition, which is well supported by the DSC measurements. Value of loss tangent in the temperature region 330–400 K is found to be very low. Activation energies for the conduction process are calculated along the a, b and c‐axes. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure and properties of antimony-doped potassium titanyl phosphate single crystals

Antimony-doped potassium titanyl phosphate (KTP) crystals of the composition KTiOPO₄ are studied by X-ray diffraction analysis. It is shown that, with an increase of antimony content in KTP crystals, the occupancies of potassium positions change and new additional positions for potassium atoms arise. The formation of additional vacancies and splitting of the potassium-cation positions explain the considerable decrease in the temperature of the ferroelectric phase transition, enhancement of the relaxation phenomena, and an increase in electric conductivity of antimony-doped KTP crystals. Substitution of antimony atoms for titanium is accompanied by elongation of short and shortening of long Ti-O bonds in the TiO₆ octahedra, processes which result in lower intensity of second-harmonic generation in laser-irradiated KTP crystals.     

Structure and properties of single crystals of tin-doped potassium titanyl phosphate

Single crystals with the compositions KTi_0.47Sn_0.53OPO₄ and KTi_0.25Sn_0.75OPO₄ were grown by spontaneous crystallization from flux in the K₂O-TiO₂-SnO₂-P₂O₅ quaternary system, and their structures were established from precision X-ray diffraction data. The incorporation of tin into the crystals lowers the asymmetry of cation positions in the (Ti,Sn)O₆ octahedra. The addition of even a small amount (x < 0.4) of tin to the K(Ti_{1 ? x} Sn_x)OPO₄ crystals causes fast symmetrization of the octahedra. The process slows down with an increase in the tin content until the attainment of the composition KSnOPO₄ and localization of tin in the centers of octahedra. It is these structural features that are responsible for a decrease in the optical nonlinearity of the crystals and in the intensity of second harmonic generation by laser radiation in these crystals.     

Growth and characterization of calcium hydrogen phosphate dihydrate crystals from single diffusion gel technique

Calcium hydrogen phosphate dihydrate (CaHPO₄·2H₂O, CHPD) a dissolved mineral in urine is known to cause renal or bladder stones in both human and animals. Growth of CHPD or brushite using sodium metasilicate gel techniques followed by light and polarizing microscopic studies revealed its structural and morphological details. Crystal identity by powder x‐ray diffraction confirmed the FT‐IR and FT‐Raman spectroscopic techniques as alternate methods for fast analysis of brushite crystals which could form as one type of renal stones. P‐O‐P asymmetric stretchings in both FT‐IR (987.2, 874.1 and 792 cm^‐1) and FT‐Raman (986.3 cm^‐1, 1057.6 cm^‐1 and 875.2 cm^‐1) were found as characteristics of brushite crystals. Differential Scanning Calorimetry (DSC) analysis revealed brushite crystallization purity using gel method by studying their endothermic peaks. This study incorporated a multidisciplinary approach in characterizing CHPD crystals grown in vitro to help formulate prevention or dissolution strategy in controlling urinary stone growth. Initial studies with 0.2 M citric acid ions as controlling agent in the nucleation of brushite crystals further support the presented approach. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of pure and doped lead hydrogen phosphate single crystals in silica gel

Following the chemical reaction method pure and doped lead hydrogen phosphate single crystals were grown in silica gel using different gel density, various concentrations of phosphoric acid, and lead nitrate solutions. As the gel pH plays an important role in the formation of different H₃PO₄ species in the phosphoric acid system, the pH range in which HPO ions dominate, was considered which in turn in necessary for the growth of lead hydrogen phosphate crystals. Characteristics of these crystals were carried out by infrared spectral analysis and microhardness study.     

Bridgman growth and properties of potassium lithium niobate single crystals

Transparent KLN crystals 10mm in diameter and 25 to 45mm in length have been grown by the modified vertical Bridgman technique from different melts in the range of 3035mol% K₂O, 1723mol% Li₂O and 4350mol% Nb₂O₅. The growth conditions are a growth rate of less than 0.25 mm/hr, temperature gradient in solid-liquid interface of 23 °C/mm and growth direction of <110>. As-grown KLN crystals have tetragonal tungsten bronze structure. Most of the as-grown crystals do not crack when cooling through the paraelectric/ferroelectric phase transition. 180° domain structures are observed after the KLN crystal was etched in boiling 2HNO₃:Hf. Dielectric properties and transmission spectrum of the as-grown KLN crystals are measured.     

FTIR spectroscopic,thermal and growth morphological studies of calcium hydrogen phosphate dihydrate crystals

Calcium hydrogen phosphate dihydrate (CHPD or DCPD) is found quite frequently in urinary calculi (stones). The CHPD crystals were grown by the single diffusion gel growth technique in sodium metasilicate gel. The crystals were found to be having platelet and broad needle type morphologies. The crystals were analyzed by FTIR spectroscopy. The thermal properties were studied by employing the thermogravimetric analysis. Various kinetic and thermodynamic parameters for dehydration were estimated. The selected platelet was studied by SEM for the growth morphologies indicating that the crystals grew in the form of leaflets having prominent (010) faces. This was in agreement with earlier reported studies. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Indentation deformation of magnesium orthosilicate single crystals

The variation in the microhardness of the magnesium orthosilicate crystals has been determined using Vicker's microhardness indentor. The length of the rays of dislocation rosettes around the indentation, obtained by etching the indented cleavages have been measured. It is observed that: (i) irrespective of the relative orientation of the indentor and the crystal, the median vents initiated at the sharp indentation edges, (ii) the microhardness of the crystals depends on the applied load, and (iii) the microhardness of the crystal is independent on the duration of loading. The implications are discussed.     

The growth and mechanical properties of paratellurite single crystals at high temperatures

α-TeO₂ single crystals have been grown by the Czochralski method on specially developed systems with automatic growth control. The mechanical properties of crystals under compression in the [100], [110], and [221] directions at a constant strain rate of about 10⁻⁴ s⁻¹ in the temperature range T = 733−993 K have been investigated. The distribution of plastic shear strain in deformed samples is has been experimentally studied. Manifestations of localized strain in covalent paratellurite crystals at T > 900 K are revealed for the first time. The active slip systems along which localized shear band are oriented are determined. The temperature dependence of the critical stress of transition to localized flow is investigated.     

Optical and dielectric studies on succinic acid single crystals

Single crystals of ferroelectric succinic acid (SA) with very high degree of transparency were grown from aqueous solution by slow evaporation technique. Single crystal X‐ray diffraction analysis reveals that the crystal belongs to monoclinic system with the space group P2₁/c. Some physical parameters have been determined for grown crystal. The optical absorption study reveals the transparency of the crystal in the entire visible region and the cut off wave length was found to be 240 nm. The optical band gap is found to be 3.75 eV. The dependence of extinction coefficient (k) and refractive index (n) on the wavelength have also been reported. The presence of functional groups was determined qualitatively by using Fourier transform infrared spectrum (FTIR) from which force constant has been calculated. The dielectric constant was also studied as a function of frequency at room temperature and electrical conductivity has been calculated from the Cole‐Cole plot. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,properties, and structure of potassium titanyl phosphate single crystals doped with hafnium

Single crystals of potassium titanyl phosphate doped with hafnium are grown by spontaneous flux crystallization. Their physical properties are studied, and the structure of three KTi_{1 − x} Hf _x OPO₄ crystals (x = 0.01, 0.03, and 0.12) is determined. In the crystals studied, hafnium mostly occupies the second titanium position. The doping of KTP crystals with hafnium results in an elongation of K-O bonds in the potassium polyhedra and, as a consequence, in a considerable (by approximately 180°C) decrease in the temperature of ferroelectric phase transition. The magnitude of anomalous permittivity substantially decreases. The electrical conduction in the specimens studied decreases by approximately half an order of magnitude in the low-temperature region but remains almost unchanged in the high-temperature region. Even at minor concentrations, the presence of a hafnium additive in the specimens considerably (by 35%) enhances the intensity of the second harmonic generation of laser radiation.     

Stacking faults in deformed zinc and magnesium single crystals

Using the transmission electron microscopy dissociated dislocations containing stacking faults were observed in Mg single crystals, deformed in (0001) <1120> slip system, and in Zn single crystals deformed in {1122} <1123> slip system. The overlapping flat stacking faults lying in {1102} planes and dissociated triple nodes in (0001) planes are observed in Mg. In Zn flat stacking faults are found in {112 2} planes. The value of stacking fault energy γ has been determined in Mg crystals (γ ⋍ 10 erg/cm²). Such a low value of γ is attributed to the segregation of impurities on dislocations.     

Dielectric studies of lead nitrate phosphate single crystals

Ferroelectric Lead Nitrogen Phosphate (LNP) single crystals have been synthesized using the controlled reaction between lead nitrate and orthophosphoric acid solutions by slow diffusion process in silicagel medium. The colourless transparent LNP crystals upto 6 × 4 × 3 mm³ in size have been grown at room temperature. The dielectric measurements have been carried out in the temperature range between 300 to 690 K. The effect of applied frequency on the dielectric constants and dielectric losses has been investigated. It has been observed that the mechanism of the dielectric behaviour is different in the lower and higher frequency and temperature ranges. The activation energy of the oscillators has been calculated and found to be 1.125 eV. Attempt has been made to draw some qualitative conclusions, taking in view, the existing theories of various kinds of polarizations and implications.     

Triglycine sulphate single crystals growing doped with copper and cobalt ions and study of their dielectric properties

Growing conditions for TGS single crystals doped with Cu or Co ions are given in a table. ε and tg δ values in growth pyramids depend on crystal growing temperature and the incorporated impurity: Cu²⁺ ions increase the temperature hysteresis of the dielectric permeabilty. Incorporation of Cu²⁺ and Co²⁺ ions considerably decreases the difference in the values ε at 25°C in crystals grown at different temperature.