Chemical vapour transport of transition metal oxides (III) crystal growth of Ti1−xRuxO2 and doped TiO2

Single crystals of the system Ti_1?xRu_xO₂ have been prepared by chemical vapour transport in closed ampoules using halide transport agents. The crystals are single phased for x ≦ 0.02 and 0.98 ≦ x. In the intermediate range a highly ordered two phased system is found. The pure RuO₂ crystals are substantially larger than any grown by open sysem chemical vapour transport. Single crystals of TiO₂ doped with other impurities have also been prepared.     

Etching behavior of CdTe,CdTe〈Ge〉, CdTe〈Sn〉, and CdTe〈Pb〉 single crystals in aqueous (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>Cr<Subscript>2</Subscript>O<Subscript>7</Subscript>-HBr-citric acid solutions

We have studied the dissolution behavior of undoped and Group IV (Ge, Sn, and Pb) doped cadmium telluride single crystals in aqueous (NH₄)₂Cr₂O₇-HBr-citric acid solutions, constructed dissolution rate-etchant composition diagrams, and located the composition regions of polishing, selective, and non-polishing solutions. The doping effect on the chemical etching process has been examined, and the rate-limiting steps in the chemical dissolution of the materials studied have been identified. We have assessed the surface condition of the etched crystals by microstructural analysis and surface profilometry and optimized the etchant composition for the dynamic chemical polishing of these semiconductors.     

Resistivity Studies on Different Variants of κ-(BEDT-TTF)2Cu[N(CN)2]Br: Evidence for Disorder and /or Defect-Induced Inelastic Scattering Contributions

Comparative resistivity measurements have been performed on differently prepared κ-(ET)₂Cu[N(CN)₂]Br single crystals. While the T_c values and their shifts under hydrostatic pressure are found to be sample independent, the resistivity profiles, especially around the resistivity hump at 90 K and the low-temperature ρ ∝ T² behavior, show striking sample-to-sample variations. In the absence of significant differences in the crystals’ structural parameters and chemical compositions, as proved by high-resolution X-ray and electron-probe-microanalysis studies, these results indicate that real structure phenomena, i.e. disorder and/or defects, strongly affect the inelastic scattering in these molecular conductors.     

Resistivity studies on different variants of κ-(BEDT-TTF)2Cu[N(CN)2]Br: Evidence for Disorder and/or defect-induced inelastic scattering contributions

Comparative resistivity measurements have been performed on differently prepared κ-(ET)₂Cu[N(CN)₂]Br single crystals. While the T_c values and their shifts under hydrostatic pressure are found to be sample independent, the resistivity profiles, especially around the resistivity hump at 90 K and the low-temperature ρ ∝ T² behavior, show striking sample-to-sample variations. In the absence of significant differences in the crystals’ structural parameters and chemical compositions, as proved by high-resolution X-ray and electron-probe-microanalysis studies, these results indicate that real structure phenomena, i.e. disorder and/or defects, strongly affect the inelastic scattering in these molecular conductors.     

Cu magic angle spinning (MAS) nuclear magnetic resonance (NMR) study of CuX crystals (X=Cl, Br, and I) and CuX-based glasses (X=Cl, Br, and I)

⁶³Cu MAS NMR spectra of CuX crystals (X=Cl, Br, and I) and CuX-based glasses (X=Cl, Br, and I) have been measured. The CuCl and CuI crystals gave the isotropic chemical shift values around 0 ppm, and the CuBr crystal, around −55 ppm. The peak positions of the chlorocuprate(I), bromocuprate(I), and iodocuprate(I) glasses were very close to those of the CuX crystals, respectively. This result indicates that these glasses mainly consist of CuX₄ tetrahedra (X=Cl, Br, and I). The halogen coordination environments around Cu⁺ in bromochlorocuprate(I) glasses were dependent on the kind of modifying cation and the Br⁻/(Cl⁻+Br⁻) ratio. The bromochlorocuprate(I) glasses were mainly composed of CuCl_mBr_4−m or CuCl_nBr_4−n tetrahedra (m=0, 1, 2, and 4; n=0, 1, and 4).     

Crystal growth and structural analysis of zirconium sulphoselenide single crystals

A series of zirconium sulphoselenide (ZrS _x Se_3−x , where x = 0, 0·5, 1, 1·5, 2, 2·5, 3) single crystals have been grown by chemical vapour transport technique using iodine as a transporting agent. The optimum condition for the growth of these crystals is given. The stoichiometry of the grown crystals were confirmed on the basis of energy dispersive analysis by X-ray (EDAX) and the structural characterization was accomplished by X-ray diffraction (XRD) studies. The crystals are found to possess monoclinic structure. The lattice parameters, volume, particle size and X-ray density have been carried out for these crystals. The effect of sulphur proportion on the lattice parameter, unit cell volume and X-ray density in the series of ZrS _x Se_3−x single crystals have been studied and found to decrease in all these parameters with rise in sulphur proportion. The grown crystals were examined under optical zoom microscope for their surface topography study. Hall effect measurements were carried out on grown crystals at room temperature. The negative value of Hall coefficient implies that these crystals are n-type in nature. The conductivity is found to decrease with increase of sulphur content in the ZrS _x Se_3−x series. The electrical resistivity parallel to c-axis as well as perpendicular to c-axis have been carried out in the temperature range 303–423 K. The results obtained are discussed in detail.     

Growth and characterization of Pb0.97La0.02(Zr0.66Sn0.27Ti0.07)O3 antiferroelectric single crystals

Single crystals of Pb_0.97La_0.02(Zr_0.66Sn_0.27Ti_0.07)O₃ (PLZST) with the composition near the morphotropic phase boundary were grown by the flux method. The PbO–PbF₂–B₂O₃ system was used as a solvent. PLZST single crystals with the size of 4–6 mm are obtained and these crystals are slightly translucent after polishing. The splitting of (200) reflection peak indicates that the obtained crystals are of a single phase with tetragonal perovskite structure. The element contents of the grown crystals were measured by inductively coupled plasma atomic emission spectrometry. The chemical composition of the crystals is Pb_0.979La_0.014(Zr_0.666Sn_0.285Ti_0.049)O₃. Thermal properties and dielectric properties of PLZST single crystals were studied. The results show that flux-grown PLZST single crystals exhibit obvious endothermic processes and relaxor behaviors near the phase transition temperatures.     

Crystal Growth and Properties of (CuInSe2) x (2ZnSe)1 – x Solid Solutions

(CuInSe₂) _x (2ZnSe)_{1 – x} crystals are grown by the horizontal Bridgman process and chemical vapor transport, and their composition and structure are determined. The transmission and reflection spectra of the crystals are measured near the intrinsic edge. The results are used to determine the band gap of the (CuInSe₂) _x (2ZnSe)_{1 – x} solid solutions, which is found to vary nonlinearly with composition.     

Solid-state photochemistry of platinum(II) methylazide complexes as thin films on Si (111) surfaces: photolithography of platinum films

The solid-state photochemistry of L₂Pt(Me)(N₃) (L=PPh₃, PEt₃, dppe/2) have been investigated on Si (111) surfaces. Photolysis of an amorphous thin film of L₂Pt(Me)(N₃) results in the loss of all ligands. This occurs via a single photon process with no detectable thermally stable intermediate. The resultant films are primarily platinum metal although some phosphine-containing impurity remains. The final analysis leads to formulations of the films as Pt(dppe)_0.06, Pt(PPh₃)_0.12 and Pt(PEt₃)_0.07. The thicknesses of the platinum films ranged from 150 nm to less than 25 nm. This process was shown to be compatible with standard lithography methods by the production of 3 μm wires on Si (111) by photolithography.     

Chemical vapor transport growth of vanadium(IV) selenide and vanadium(IV) telluride single crystals

A process for the growth of VSe₂ and VTe₂ single crystals using VCl₃ as a transport agent is proposed and experimentally demonstrated. X-ray diffractometry and Laue X-ray photography results indicate that the crystals thus grown are identical in properties to chalcogenide crystals grown using I₂ as a transport agent. The mechanism of chemical vapor transport is discussed and the process conditions are optimized.     

Charge transport and mechanisms of electron scattering in (HgSe)3(In2Se3) crystals doped with 3d transition metals

We have studied the transport properties of (HgSe)₃(In₂Se₃), (HgSe)₃(In₂Se₃)〈Mn〉, and (HgSe)₃(In₂Se₃)〈Fe〉 crystals and identified the predominant mechanisms of electron scattering in them. The transport properties of the (HgSe)₃(In₂Se₃) crystals, undoped and doped with 3d transition metals, have been studied by the four-probe technique. The results demonstrate that the Hall coefficient of the crystals is temperature-independent, their electrical conductivity shows metallic behavior and is an almost linear function of temperature, and their thermoelectric power increases with increasing temperature.     

Growing high-quality Bi12SiO20 crystals of large diameter (85 mm)

Conditions that ensure reproducible growth of ??110??-oriented perfect Bi₁₂SiO₂₀ (BSO) crystals by the low-thermal-gradient Czochralski technique, whereby the entire crystallization front is occupied by the (110) crystal face, have been determined with the aid of numerical simulations. Using the established regime, BSO crystals have been obtained with a diameter of 85 mm, a length of 200 mm, and a mass of 10 kg. The density of dislocations in the crystals does not exceed 10 cm^?2, and the refractive index inhomogeneity is below 10^?3.     

Transport properties of MoSe x Te2−x (0 ≤x ≤ 2) single crystals

The layer type MoSe _x Te_2−x (0 ≤x ≤ 2) have been grown in single crystalline form by chemical vapour transport technique using bromine as the transporting agent. The electrical resistivity and Hall mobility perpendicular to thec-axis of the crystals were measured at room temperature. The variation of the Seeback coefficient with temperature was also investigated.     

Preparation and crystal growth of NiS(h)

A procedure is described for the preparation of 90 g batches of NiS. Molten NiS has been shown to exert a pressure of about 9 atm of sulphur and to be compatible with liquid B₂O₃. Near single crystals of NiS(h) have been grown by the high pressure liquid encapsulated Czochralski technique. Evidence suggests that the as-grown crystals exhibit variable stoichiometry and an annealing procedure which gives apparently homogeneous samples is described.     

Synthesis and crystal growth of new antimony(III)-oxide-iodides

In the system Sb₂O₃1bSbI₃, compounds with Sb₂O₃:SbI₃ ratios of 14:2, 11:2 and 8:2, i.e. Sb₅O₇I, Sb₈O₁₁I₂ and Sb₃O₄I have been synthesized. Colorless single crystals of mm dimensions were grown by vapour transport and characterized by chemical, thermal and X-ray analysis. The latter revealed the existence of at least two more phases with higher iodine contents.     

Growth of MBO3 (M = La, Y, Sc) and LaSc3(BO3)4 crystals from LiBO2-LiF fluxes

The solubility of rare-earth orthoborates and LaSc₃(BO₃)₄ in LiBO₂-LiF solvents has been studied. Spontaneous crystals have been grown and the solvent used has been shown to be attractive for the growth of bulk crystals at t ≤ 1000°C. The α- and γ-phases of LaSc₃(BO₃)₄ have been shown to be identical.     

Chemical interaction of InAs,InSb, GaAs,and GaSb crystal surfaces with (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>Cr<Subscript>2</Subscript>O<Subscript>7</Subscript>–HBr–citric acid etching solutions

We have studied the chemical dissolution of InAs, InSb, GaAs, and GaSb crystals in (NH₄)₂Cr₂O₇–HBr–C₆H₈O₇ solutions. The dissolution rate of the crystals has been measured as a function of etchant composition, and the kinetics of the chemical interaction of the semiconductors with solutions have been investigated in detail. The dissolution rate has been shown to be diffusion-limited. Citric acid helps to reduce the etch rate and improves the polishing performance of the etching solutions.     

Electron microscopy of layered single crystals grown by direct vapour transport method

Besides interesting properties such as optical, transport, structure, etc. possessed by crystals of transition metal dichalcogenides, they have also been found to have a potential application in the fabrication ofpec solar cells. These crystals are normally grown by carrier gas transport technique but are always contaminated by carrier gases. A new method of direct vapour transport has been developed and successfully applied to grow these crystals including those of off-stoichiometric varieties. The crystals thus grown have been characterized structurally using the techniques of x-ray powder, rotation and Weissenberg photographs and electron diffraction. Perfection studies have been made by techniques like chemical etching and electron microscopy. This review describes the electron microscopic studies made on the single crystals of the layered compounds. High resolution technique of weak beam has been employed to study dislocation pattern. Dissociated dislocations have been used to estimate stacking fault energy. Such measurements have also been carried out at different temperatures and the variation of stacking fault energy with temperature has been worked out. Interesting information regarding phase transformation for TaS₂ and W₃Se₄ in the temperature range 109 to 580 K has been derived from the electron diffraction studies and the implications have been discussed.     

Phase separation during the melting of oxide borates LnCa4O(BO3)3 (Ln=Y, Gd)

GdCa₄O(BO₃)₃ (GdCOB) and YCa₄O(BO₃)₃ (YCOB) single crystals have been grown from the melt by the Czochralski method. Subsequent DTA analysis of the single crystals showed different behavior for both substances. During the first heating both crystals showed a single sharp melting peak at 1490°C (GdCOB) or at 1504°C (YCOB), respectively. In subsequent heating/cooling runs only GdCOB shows one single peak, whereas YCOB shows five peaks. Moreover, phase separation of the melt can be observed by optical observation and by EDX measurements. This behavior can be explained by a miscibility gap in the YCOB melt. The YCOB crystal is formed from the stoichiometric melt by a monotectic reaction.     

Growth and some properties of barium-cadmium formate single crystals: (I) Crystal growth and morphology

The growth of barium-cadmium formate BaCd(HCO₂)₄·2H₂O single crystals by slow cooling method and their characterization by selective etching are reported. It was found that BaCd(HCO₂)₄·2H₂O crystallizes from aqueous solution in 2/m class of the monoclinic system. Crystals grown during a period of 1 month have dimensions of about 2 × 1.5 × 10 cm³. The typical twinning for these crystals has been observed and investigated by the selective etching. The dislocation density has been estimated to be 3·10² – 2·10³ cm^?2.