Structural and magnetic properties of ZnO and Zn1−xMnxO nanocrystals

Chemical precipitation of metal-ions from aqueous solution has been successfully used to produce Zn_1?xMn_xO nanocrystals, in the form of nano-powder. X-ray diffraction (XRD) measurements reveal that the as-prepared samples are single-phase materials and their lattice constant changes with the variation of Mn-concentration, which indicates the incorporation of Mn²⁺ into the hosting ZnO. These findings are corroborated by the observation of the well defined six hyperfine lines of Mn²⁺ ion in the electron paramagnetic resonance (EPR) spectra of the samples with a low Mn-concentration, and of a broad EPR line, which manifests the onset of Mn–Mn exchange interaction, in the samples with an elevated value of x.     

Growth and characterization of InxBi2−xTe3 single crystals

The V–VI group narrow band gap compounds are known to have important photoconductivity and thermoelectric properties. Among these, Bi₂Te₃ is the most potential material for thermoelectric devices having a direct band gap of 0.16 eV. There has been ample study reported on crystal growth and polycrystalline thin films of both pure and indium doped Bi₂Te₃ pertaining to its basic semiconducting, optoelectronic and thermoelectric properties. It has been shown that on exceeding certain limiting concentration of indium in Bi₂Te₃, the conductivity changes from p-type to n-type. However, there is hardly any work reported in literature on crystal growth, dislocation etching and optical band gap of In_xBi_2?xTe₃ (x=0.1, 0.2, 0.5) single crystals. The authors have grown their single crystals using the zone melting method. The freezing interface temperature gradient of 70 °C/ cm^?1 has been found to yield the best quality crystals obtainable at the growth rate of 0.4 cm/h. The as-grown crystals have been observed to exhibit certain typical features on their top free surfaces. The crystals have been characterized using XRD technique. A chemical dislocation etchant has been used for estimating perfection in terms of dislocation density in the crystals. The optical absorption was measured in the wave number range 500 to 4000 cm^?1. The transitions in all the cases were observed to be allowed direct type. The detailed results are reported in the paper.     

Growth improvement and characterization of AgGaxIn1−xSe2 chalcopyrite crystals using the horizontal Bridgman technique

AgGa_xIn_1?xSe₂ single crystals with x=0.4 have been grown by the horizontal Bridgman technique for nonlinear optical application requires phase matching. High purity polycrystalline synthesis of AgGa_xIn_1?xSe₂ was carried out at 850 °C, which is a relatively lower temperature compared to those in earlier reports, thus reducing secondary phase formation. An average Ga:In ratio of 62:38 (±3%) was measured using energy dispersive spectroscopy (EDS). As grown, a single crystal shows very high IR transmission of ～65% in the spectral range of 4000–600 cm^?1. There was no significant change in its IR transmission after annealing it at 500 °C for 20 days in vacuum in the presence of AgGa_xIn_1?xSe₂ powder. This indicates a low concentration of defects in the crystal. The results demonstrate that the improved new synthesis method for crystal growth was promising and that the quality of the crystal was good.     

Growth and study of single crystals of Pb1 − x BaxSc0.5Nb0.5O3 solid solutions

Crystals of Pb_{1 ? x} Ba_xSc_0.5Nb_0.5O₃ solid solutions with 0 ≤ x ≤ 0.58 have been grown by the method of mass crystallization from flux. It is established that, unlike the concentration dependence of the corresponding ceramic, the concentration dependence of the temperature T _m (the maximum dielectric constant ε in crystals) does not attain saturation. Cooling of crystals with x ≤ 0.04 resulted in a spontaneous transition from the relaxor to the macrodomain ferroelectric state. In crystals with a higher barium content, the relaxor state is “locked in.”     

Growth and properties of mixed K2Ni x Co1−x (SO4)2 · 6H2O crystals

Optically homogeneous mixed K₂Ni _x Co_{(1 ? x)}(SO₄)₂ · 6H₂O crystals are grown from solutions of different compositions by the temperature-reduction technique in static and dynamic regimes. The optical characteristics of the grown crystals are measured: transmittance reaches 80% in the wavelength range of 240–290 nm and no more than 9% in the visible spectral range. The thermal stability of the crystals is studied. It is established that the thermal stability of mixed K₂Ni _x Co_{1 ? x} (SO₄)₂ · 6H₂O crystals is higher than that of K₂Co(SO₄)₂ · 6H₂O crystal. The defects of the mixed crystals grown in static and dynamic regimes are investigated by X-ray topography.     

Growth of CuSO4 · 5H2O single crystals and study of some of their properties

Large single crystals of copper sulfate pentahydrate CuSO₄ · 5H₂O of optical quality have been grown; they can be applied as broadband UV optical filters. Their transmission spectra are measured. The crystal thermal stability is investigated and the onset temperature of dehydration is determined to be 46°C.     

Electromechanical and electro-optic properties of xBiScO3–yBiGaO3–(1−x−y)PbTiO3 single crystals

Single crystals in the xBiScO₃–yBiGaO₃–(1−x−y)PbTiO₃ (BS–BG–PT) system were grown by the high temperature solution method using Pb₃O₄ and Bi₂O₃ as the flux. The dielectric permittivity (ε_r) at room temperature for unpoled tetragonal crystals was determined to be 500–600 with dielectric loss tangents less than 0.3%. The Curie temperature was found to be around ∼420–450°C, with a dielectric maximum, exhibiting relaxor behavior. The longitudinal piezoelectric coefficient (d₃₃) was found to be ∼300 pC/N for 〈0 0 1〉 oriented tetragonal crystals with electromechanical coupling factor (k₃₃) of 75%, with a shear mode, d₁₅∼290 pC/N and k₁₅∼45%, lateral mode, d₃₁∼−55 pC/N and k₃₁∼−37%. The remnant polarization (P_r) was 46 μC/cm² with a coercive field (E_c) of 43 kV/cm at 1 Hz and DC field of 60 kV/cm. The linear electro-optic (E-O) coefficients of poled crystals determined using an automated scanning Mach–Zehnder interferometer method at room temperature and wavelength of 632.8 nm were r₃₃=36 and r₁₃=4 pm/V, respectively.     

Growth of Ga x In1 − x Sb solid solution single crystals by the Czochralski method

Crystallography Reports - Ga x In1 ? x Sb solid solution single crystals (x = 0.03–0.09) have been grown. The dislocation density and electrophysical parameters are measured. A...     

Growth of Er2(SO4)3 ⋅ 8H2O crystals and study of their structure and properties

New crystals of the composition Er₂(SO₄)₃ ? 8H₂O have been synthesized by the method similar to that used for synthesis of (CH₃)₂NH₂Al(SO₄)₂ ? 6H₂O. The synthesized crystals were studied by the X-ray diffraction method. The crystals are monoclinic C2/c) and contain no (CH₃)₂NH₂ ions. It is established that, contrary to DMAAS crystals, Er₂(SO₄)₃ ? 8H₂O crystals undergo no phase transitions and possess neither ferroelectric nor ferroelastic properties.     

Effects of post-annealing temperature on structural,optical, and electrical properties of MgxZn1−xO films by RF magnetron sputtering

Mg_xZn_1?xO thin films were deposited on quartz substrates by RF magnetron sputtering. The effect of post-annealing temperature on structural, optical, and electrical properties was investigated with the annealing temperatures increasing from 450 to 750 °C. The crystallinity of Mg_xZn_1?xO film annealed at 650 °C was significantly improved while the film annealed at 750 °C showed little improvement. The electrical properties degraded with the increase of annealing temperature. The annealing temperature seemed to impact the E_g value of Mg_xZn_1?xO thin films because of the variation of carrier concentration.     

Raman investigation of ZnO and Zn1−xMnxO nanocrystals synthesized by precipitation method

Zn_1?xMn_xO nanocrystal samples have been successfully synthesized using the chemical precipitation method in aqueous solution. Comparing with pure ZnO NC, the Raman data recorded from the manganese-doped nanocrystals shows an enhancement of the peaks located at 334 and 439 cm^?1. Besides, a new feature at 659 cm^?1 emerges. X-ray diffraction (XRD) of the as-precipitated nanocrystal samples illustrates that Mn-doping only makes the XRD peaks of the as-precipitated Mn-doped nanocrystals shift towards lower angle values, but the crystal structure of bulk ZnO is still preserved in the Mn-doped samples. Hence, the high quality Zn_1?xMn_xO (x ? 0) nanocrystals are formed through the replacement of zinc ions by manganese ions.     

Growth and characterization of lead-free Ba(1−x)CaxTi(1−y)ZryO3 single crystal

A lead-free Ba_(1?x)Ca_xTi_(1?y)Zr_yO₃ (BCZT) single crystal (x=0.08, y=0.26) was grown by the Czochralski (CZ) method in a mixed flux of TiO₂ and ZrO₂. The composition of as-grown BCZT was analyzed by electron probe micro-analysis. The structure, dielectric properties and phase transition were investigated at different temperatures. The X-ray diffraction results confirmed that the structure of the as-grown BCZT crystal was cubic both at 25 °C and 500 °C. The temperature dependence of the dielectric constant and Raman spectra characterization revealed that there was a phase transition from cubic to tetragonal, which happened between 200 K and 250 K. With increasing frequency, the Curie temperature shifted towards high temperature.     

Growth,structural, optical and thermal properties of potential THz material: N,N-dimethylamino-N′-methylstilbazolium 4-styrenesulphonate

N,N-dimethylamino-N′-methylstilbazolium 4-styrenesulphonate (DSSS), was synthesized by metathesization of the N,N-dimethylamino-N′-methylstilbazolium iodide (DASI) salt with sodium 4-styrenesulfonate. The growth of DSSS single crystal was carried out by adopting the slope nucleation coupled slow evaporation method. DSSS crystals with size 4×2×1 mm³ were grown within a period of 15 days. The structure and composition of the crystal were studied by single crystal X-ray diffraction, CHN and nuclear magnetic resonance (NMR) analyses. The FTIR results reveal the existence of the vinyl groups and their corresponding vibrational modes. The melting point and thermal behavior of DSSS were investigated using differential scanning calorimetric (DSC) and thermogravimetric analyses (TGA).     

Growth rates of the principal facets of ice between −10°C and −40°C

We describe measurements of the growth rates of the basal and prism facets of ice crystals grown from the vapor phase at temperatures −39°C<T<−10°C. We find that all our data can be well described by a model in which the facet growth is limited primarily by 2D nucleation over this temperature range. The inferred critical supersaturations, and thus the step edge free energies, are essentially identical for the two facets, with values that decrease monotonically with increasing temperature. The growth scaling parameters, on the other hand, exhibit a more complex behavior with temperature that is quite different for the two facets. These data suggest that much of the peculiar behavior seen in ice crystal growth from vapor is due to differences in the surface diffusion of admolecules on the two principal facets.     

Growth, structure, and properties of ferroelectric—ferroelastic— superionic K3Nb3B2O12 and K3−x NaxNb3B2O12 crystals

The potassium niobate-borate K₃Nb₃B₂O₁₂ (KNB) crystals and their solid solutions with partial substitution of potassium by sodium (KNB: Na) are grown from flux and their physical properties are studied. The specific feature of the crystals grown is a complicated polymorphism and the unique combination of ferroelectric and ferroelastic properties with superionic conductivity with respect to potassium ions.     

Investigation of the structure and properties of (K x (NH4)1 − x )3H(SO4)2 single crystals

The influence of isomorphous replacement in the cation sublattice on the kinetics of the phase transition in single crystals of the solid solutions (K _x (NH₄)_{1 ? x} ) _m H _n (SO₄)_{(m + n)/2} · yH₂O belonging to the K₃H(SO₄)₂-(NH₄)₃H(SO₄)₂-H₂O salt system was studied. Superproton phase transitions for the end compositions of this system have been found earlier. The optical and thermal properties of crystals with the composition (K,NH₄)₃H(SO₄)₂ in the temperature range from 295 to 500 K were investigated, and the crystal structure was determined at 295 K. The results of the study and the comparison with the literature data show that the replacement of potassium atoms with ammonia leads to a fundamental change in the kinetics of the phase transition, the phase-transition temperature remaining virtually unchanged.     

Growth and structure of epitaxial Pb1 − x Mn x Se(Ga) films

The growth and structure of Pb_{1 ? x} Mn _x Se (Ga) (N_Ga = 0.8 at %) films with thicknesses of 0.3–0.5 μm, grown on single-crystal PbSe_{1 ? x} S _x (100) substrates by molecular-beam epitaxy, have been studied. It is established that films grow in a face-centered cubic lattice with the (100) orientation, reproducing the substrate orientation. The optimal conditions for obtaining photosensitive epitaxial films with perfect crystal structure are determined (W _1/2 = 70–80″).

     

Elastic, piezoelectric, and dielectric properties of α-GeO2 single crystals

The elastic, piezoelectric, and dielectric characteristics of α-GeO₂ crystals are studied at room temperature. The measurements were performed by the resonance method on crystals grown on α-quartz seeds from solutions in the recirculating mode. In germanium dioxide crystals, the piezoelectric moduli have high values. The characteristic features of variations of the electromechanical and elastic properties in crystals with the quartzlike structure observed earlier are confirmed.