Gallium phosphide is a typical III–V compound semiconductor and is also an important electronic material. The synthesis and single crystal growth of this compound by melt methods is rendered very difficult because of the large phosphorus vapour pressure. A high pressure vessel with internal heating and a quartz reactor was first developed for the direct synthesis of gallium phosphide. The crystal growth was carried out in a second high pressure chamber rated for 100 bars gas pressure and equipped with the paraphernalia for crystal growth. Single crystals of gallium phosphide were grown from the polycrystalline starting material by the vertical Bridgman method and the vapour pressure problem was overcome by encapsulating the melt in a column of molten boric oxide. Both boron nitride and silica were employed as crucibles, and with the former, single crystal rods of 8–10 mm diameter and 10–15 mm length were obtained.

We report an elegant method for the synthesis of single-phase Bi-2223 superconductor from a stoichiometric composition Bi_1.7Pb_0.3Ca₂Sr₂Cu₃O_y by a matrix reaction route. The superconducting transition temperatureT_c (R=0) of this single-phase compound is 120 K. The effect of Pb-content and sintering temperature on the formation and stability of Bi-2223 phase is described.

This paper describes the synthesis and microwave absorption studies of single phase Tl-2223 compound, withT_c=(129 ± 1) K. The single phase compound has been synthesized using a precursor matrix method. It has been found that Tl-deficient starting composition gives the best results.

We have synthesized CaBaLaCu₃O_7−δ and related compounds Ca_0.9BaLaCu₃O_7−δ, Ca₁₁ BaLaCu₃O_7−δ and Ca_0.9Ce_0.1 BaLaCu₃O_7−δ in order to investigate the effect of doping and non-stoichiometry at Ca-sites on the superconducting behaviour of tetragonal superconductor CaBaLaCu₃O_7−δ. The superconducting transition temperature (T_c) of Ca_0.9 BaLaCu₃O_7−δ is the same as that of pure CaBaLaCu₃O_7−δ(67 ± 1 K). Calcium excess compound Ca_1.1 BaLaCu₃O_7−δ showed a drop inT_c to 72 K while the cerium-substituted compound Ca_0.9 Ce_0.1 BaLaCu₃ O_7−δ showed a drop inT_c to 43 K. The results are explained on the basis of difference in valency between the host and the dopant ion.

Coherent inelastic neutron scattering measurements have been carried out on the high temperature superconductors Tl₂CaBa₂Cu₂O₈ (Tl-2122,T_c=107 K) and YBa₂Cu₃O₇ (Y-123,T_c=92 K), at the Dhruva reactor at Trombay. The density of phonon states in Tl-2122 is enhanced at 6–17 meV and reduced at 40–70meV compared to that in Y-123.

Doppler-broadened annihilation radiation spectra have been measured as a function of temperature from 77 K to 300 K, for several high temperature oxide superconductors viz single-phase YBCO, single- and mixed-phase Tl-Ca-Ba-Cu-O and Bi-Ca-Sr-Cu-O compounds. The temperature-dependent parameters extracted respond to a change at the onset of superconducting transition. The observations point to involvement of oxygen valence electrons at the onset of superconducting transition. Also a possible structural change and/or increase in electron density at the oxygen vacancy/defect sites seem to accompany the transition. In addition, the parameters derived are seen to be sensitive to the presence of more than one superconducting phases in mixed phase samples.

Single-phase 2122 samples of thallium and bismuth superconductors were made by the precursor matrix method. The thermopower of these samples was measured in the temperature range 250 K-T_c. The thermopower was positive and decreased linearly with increasing temperature aboveT_c (onset). The exponential enhancement of thermopower seen in the undoped and doped YBCO was not observed in these samples. The linear variation of thermopower can be explained on the basis of either a two-band model or a narrow band model.