Growth and electrical characterization of the lead magnesium niobate-lead titanate (PMN-PT) single crystals for piezoelectric devices

The lead magnesium niobate-lead titanate is one of the new generations of piezoelectric materials with outstanding properties. Single crystals of 0.67Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (PMN-PT) show superior properties as compared to piezoelectric ceramics and piezoelectric films in device applications. Large size crystals are required for specific applications. Previously, transparent and high quality PMN-PT single crystals have been grown in our laboratory using the high temperature flux method. The size of the obtained crystals was small and varied from 2 to 8 mm³, mostly showing regular prismatic shape. In present attempt, PMN-PT crystals are grown from the vertical gradient freeze method with no flux using congruent melt. Processing conditions and growth parameters have been optimized to increase the size and yield of the perovskite crystals including cooling rate, soak time and soak temperature. The size of the grown crystals obtained by this method is very large relatively and varied from 5 to 30 mm³. The microstructure of the as grown single crystals is investigated by scanning electron microscopy. Piezoelectric properties of the grown crystals are also investigated. PMN-PT plates show excellent piezoelectric properties. Samples were poled under an applied electric field of 5 kV/cm. Dielectric properties at a frequency of 1 kHz are examined. Finally, the variation of pyroelectric coefficient with temperature is studied. The grown PMN-PT crystals show typical relaxor dielectric properties.     

Optical and electrical properties of ZrSe3 single crystals grown by chemical vapour transport technique

Single crystals of the lamellar compound, ZrSe₃, were grown by chemical vapour transport technique using iodine as a transporting agent. The grown crystals were characterized with the help of energy dispersive analysis by X-ray (EDAX), which gave confirmation about the stoichiometry. The optical band gap measurement of as grown crystals was carried out with the help of optical absorption spectra in the range 700–1450 nm. The indirect as well as direct band gap of ZrSe₃ were found to be 1.1 eV and 1.47 eV, respectively. The resistivity of the as grown crystals was measured using van der Pauw method. The Hall parameters of the grown crystals were determined at room temperature from Hall effect measurements. Electrical resistivity measurements were performed on this crystal in the temperature range 303–423 K. The crystals were found to exhibit semiconducting nature in this range. The activation energy and anisotropy measurements were carried out for this crystal. Pressure dependence of electrical resistance was studied using Bridgman opposed anvils set up up to 8 GPa. The semiconducting nature of ZrSe₃ single crystal was inferred from the graph of resistance vs pressure. The results obtained are discussed in detail.     

Crystal growth of some rare earth trifluorides

Single crystals of GdF₃, TbF₃, DyF₃, HoF₃ and ErF₃ have been grown by using a Bridgman-Stockbarger method utilising sealed platinum crucibles. DyF₃ and HoF₃ have also been grown by the Czochralski technique.     

Growth of gallium orthophosphate single crystals in acidic hydrothermal solutions

The hydrothermal growth of GaPO₄ single crystals has been studied in several solutions. Among many solutions, H₃PO₄, HCl and H₂SO₄ solutions were found to be effective solvents for the growth of GaPO₄ single crystals. Single crystals have been hydrothermally grown at temperatures over the range 210 to 290 °C in these solutions with seed crystals. HCl solution was found to be the most effective solvent in which to grow large single crystals. Morphologies of crystals grown at temperatures below 200 °C tended to be bounded by small major rhombohedral (1 0 ˉ1 1) faces. In the temperature range from 210 to 430°C, the crystals have morphologies bounded by prism (1 0 ˉ1 0), small major rhombohedral (1 0 ˉ1 1) and minor rhombohedral (0 1 ˉ1 1) faces, and grew with well developed basal (0 0 0 1) faces with increase in the growth temperature. Single crystals of GaPO₄ with lower dislocation density have been hydrothermally grown at 210 to 290°C in 3m H₃PO₄ solution.     

Growth and characterization of some I–III–VI2 compound semiconductors

Single crystals of CulnS₂, CulnSe₂, CulnTe₂, CuGaS₂, AgGaS₂ CulnSSe, AgGaSSe have been grown by chemical vapour transport technique on the basis of a new general thermodynamical model which enables the minimum source temperature T _s, and the minimum deposition temperature, T _d, to be determined. X-ray analysis, X-ray photoelectron spectroscopic analysis, surface analysis, and microhardness studies have been carried out on the single crystals grown.     

Polymorphism in the rare-earth trichlorides: Phase equilibria and crystal growth measurements

Single crystals of GdCl₃, TbCl₃, DyCl₃, and HoCl₃, have been grown by the Bridgman - Stockbarger method. The phase equilibria diagrams for binary mixtures of these chlorides have been determined by DTA and X-ray measurements. Solid - state transition temperatures are recorded and the extent of stability of the structural types is discussed.     

Growth of Sb2S3 single crystals by chemical vapour transport

Single crystals of antimony trisulfide have been grown by a chemical vapour transport technique using iodine as the transporting agent. Single crystals were obtained at a much lower temperature when antimony and sulfur in the stoichiometric ratio were taken as the source along with iodine. However when polycrystalline antimony trisulfide was taken as the source with iodine, single crystals were not obtained even at the melting point of Sb₂S₃. This observation has been explained on the basis of bond energy values.     

Growth of Pr0.7Sr0.28Pb0.02MnO3 single crystals and determination of the phase transition temperature

Single crystals containing Pr_0.7Sr_0.28Pb_0.02MnO₃ were synthesized and grown. The structure and phase-transition temperature of these crystals were determined. The established Curie point temperature was 380 K. The ferromagnetic–paramagnetic transition conditions the colossal magnetoresistance of this perovskite manganite.     

Single crystals growth and magneto-thermal properties of Dy3Ga5O12 garnet

Single crystals of Dy₃Ga₅O₁₂ garnet have been grown by the Czochralski method and the anisotropy of magnetic entropy evaluated for use as a magnetic material for a magnetic refrigeration in place of Gd₃Ga₅O₁₂ single crystals. As the size of the single crystal is large enough, and the anistropy is small, this crystal is suited to use for magnetic refrigeration in the temperature range of 1.8 to 15 K.     

Studies on the growth and physical properties of nonlinear optical crystal: 2-Amino-5-nitropyridinium-toluenesulfonate

Single crystals of 2-amino-5-nitropyridinium-toluenesulfonate (2A5NPT) were grown by the slow cooling method. The unit cell dimensions were determined from single crystal X-ray diffraction studies. The thermal parameters - thermal diffusivity (α), thermal effusivity (e), thermal conductivity (K) and heat capacity (C_p) of 2A5NPT were measured by an improved photopyroelectric technique at room temperature. Single and multiple shot experiments performed on the grown crystals for the second harmonic of pulsed Nd:YAG laser (532 nm) show that it exhibits a high laser damage threshold which is a favorable property for nonlinear optical applications. Dielectric constant and dielectric loss of the grown crystal were evaluated for the frequency range 1 kHz-1 MHz in the temperature region 40-130 °C. Hardness values were measured using Vickers hardness measurement.     

Preparation and dta of some AIBIIICVI2 compounds

Single crystals of AgGaSe₂, AgGaTe₂, AgInSe₂ and AgInTe₂ were grown by a step-wise slow cooling technique. Phase transformations on the two Tellurides have been detected by DTA on powder samples.     

The growth of single crystals of the intermediate phases NiAl and Ni3Al

Single crystals of stoichiometric NiAl, nickel-rich Ni₃Al, and aluminium-rich Ni₃(Al, Ti) have been grown by a modified Bridgman technique; a strain-anneal method has also been used to produce small, single crystals of non-stoichiometric NiAl.     

Relaxor properties of single crystals of Na1/2Bi1/2TiO3-KTaO3 solid solutions

Single crystals of Na_1/2Bi_1/2TiO₃-KTaO₃ (NBT-KT) solid solutions have been grown for the first time. The elemental composition of as-grown single crystals determined by X-ray diffraction corresponds to 0.81 NBT-0.19 KT. Measurements of the temperature dependences of dielectric characteristics showed that the obtained NBT-KT crystals possess clearly pronounced relaxor properties.     

Crystal growth of Bi2Sr2CuO6 from flux system KCl-KF and its superconductivity

Single crystals of Bi₂Sr₂CuO₆ (BSCO) were grown from high-temperature solution using KCl-KF as flux. Differential thermal analysis (DTA) of the starting materials enabled an appropriate temperature programme to be introduced for crystal growth by spontaneous nucleation. By means of the improved thermogravimetric (TG) method, Bi₂Sr₂CuO₆ crystals were grown after determination of the crystallization temperature. A single crystal in the form of a thin rectangular platelet up to 6×4 mm² was obtained and was identified by X-ray powder pattern and by scanning electron microscopy (SEM). Analyses were performed by using high-resolution electron probe microanalysis (EPMA), which indicated that it is the nonstoichiometric compound Bi_2+xSr_2–xCuO₆. The superconducting properties are strongly dependent on the composition of Bi and Sr in the crystals and on heat treatment. The transition temperature of 7 K with 0.5 K width for as-grown crystals, has been obtained.     

Hydrothermal recrystallization of Bi2WO6

The feasibility of growing single crystal Bi₂WO₆ by the hydrothermal method is reported. Single domain crystals (～1mm) were readily grown at 400°C, well below the disruptive high temperature phase transformation, from 2N aqueous KF solutions. Data is given for X-ray diffraction and hot-stage microscopy observations. The significance of preparing strain-free, single domain, highly acentric polar crystals for new device applications is discussed.     

Crystal growth and characterization of PdTe2

Single crystals of PdTe₂ have been grown from the melt at a temperature of 800°C by means of a modified Bridgeman technique. Characterization studies of the crystals included density determinations and x-ray analysis. The crystals were found to be metallic, and the sign of the carriers from Seebeck measurements was ascertained to be positive.     

Microhardness studies on as-grown faces of NaClO3 and NaBrO3 crystals

Single crystals of NaClO₃ and NaBrO₃ are grown from their aqueous solutions at a constant temperature of 35°C by slow evaporation by using good quality seed crystals. Systematic microhardness studies are made on as-grown faces of these crystals at various loads. Typical cracks are observed at the corners of the impressions in NaClO₃ whereas in addition to the cracks at the corners microcracks also appeared in NaBrO₃ crystals around the impressions. The impressions formed in NaBrO₃ are not very clear as in NaClO₃, a possible mechanism for it is discussed. The work hardening index number(n) for both these crystals is around 1.6 suggesting that these are moderately harder samples. The hardness studies point out that NaBrO₃ is harder than NaClO₃ (ΔH ≈ 100 kg/mm ²,this could be due to strong inter ionic forces acting between Na-Br in NaBrO₃ crystals. Using Gilman’s empirical relation, hardness values are calculated from the values of elastic constants (C ₄₄) and are found to be close to the experimental results.     

Growth of SbI3 single crystals from vapour by the temperature oscillation method

Platelets of SbI₃ were grown from vapour by the temperature oscillatiom method. The surface features of the as grown crystals were found to depend upon temperature gradients. The grown crystals were confirmed by chemical and X-ray analysis.     

Crystal structure,magnetic susceptibility and electrical conductivity of pure and NiO-doped MoO2 and WO2

Single crystals of MoO₂ and WO₂, pure and doped with NiO, were grown by chemical transport in Vycor ampoules using iodine as the transporting agent. From X-ray diffraction analyses it was found that all the crystals were monoclinic, and that doping up to 5% does not change the unit cell constants. The pure dioxide crystals are weakly paramagnetic χ_M < 100×10^?6 emu, but doping raises the magnetic susceptibility markedly: ～ 2500×10^?6 emu. Resistance studies show that these materials are metallic conductors, the room temperature specific resistivity being of the order of 10^?4 – 10^?3 Ωcm, decreasing by one order of magnitude at liquid nitrogen temperature. Doping also substantially lowers the conductivity.