Mario D. Banus

High pressure transition in InSb

Abstract InSb (phase I) transforms at room temperature under a pressure of 23 kbars to a metallic phase (II) having a body-centered tetragonal structure with lattice constants a = 5.79 ± 0.03 and c = 3.15 + 0.03 A. An additional transition InSb I → IA was observed and was attributed to a higher order electronic transition. The InSb pressure-temperature phase diagram is discussed on a thermodynamic basis. The electrical behavior of phase II and the kinetics of the InSb I ⇄ II transformations were investigated and compared to the Sn α ⇄ β transformations. Approximate activation energies for the I → II and II → I reactions are reported and discussed in terms of various transformation mechanisms.

The P‐T Phase Diagram of InSb at High Temperatures and Pressures

The pressure‐temperature phase diagram of InSb is refined to show the boundaries between the high‐pressure tetragonal (InSb II) and orthorhombic (InSb IV) phases and extended to about 125 kbar to locate the boundary of the new phase (InSb III). The existence of these structures as stable phases in their phase fields is demonstrated by high‐pressure, high‐temperature x‐ray studies and by x‐ray studies and superconductivity measurements on these phases retained by quenching to 77°K. The structures of InSb II and InSb IV are confirmed, and a hexagonal structure for InSb III is proposed. The hexagonal cell has the dimensions (at ∼90 kbar) of a=6.10 A and c=5.71 A with a calculated density of 8.5 g/cc. Values are reported for the compressibility of phases InSb I, InSb III, and InSb IV and for the thermal expansion coefficients, under pressure, of phases InSb I and InSb IV.

High pressure phase transition in mercury selenide

Abstract It was shown by electrical resistance measurements that under pressures near 7.5 kbars and at room temperature, the zinc-blende structure HgSe transformed to a new phase. The transformation was found to be reversible although a distinct hysteresis was encountered. At low temperatures (below 170°K) the high pressure phase of HgSe was retained at atmospheric pressure and was shown by X-ray diffraction techniques to be hexagonal with a = 4.32 A, c = 9.62 A, and a calculated density of 8.95 gms cm 3 .

Nb3In: A β-tungsten structure superconducting compound

High-pressure techniques were employed to synthesize a new compound, Nbain having the β-tungsten structure (A15) with a lattice parameter a0 = 5.303 A. Its superconducting transition temperature was found to be 9.2 ± 0.1°K.

High-Pressure Transitions in A(III)B(VI) Compounds: Indium Telluride

Metallic InTe(II) has a NaCl structure with ao = 6.154 � and becomes superconducting below 3.5 � K. These results are substantially different from those previously reported. The pressure-temperature diagram to 850 � C and 50 kb is presented.

New Phase Transformation in InSb at High Pressure and High Temperature

A new phase transformation at high pressure and elevated temperature has been found in the InSb pressure‐temperature phase diagram. This transformation to a new phase designated as InSb‐III has been established by measurements of superconducting transition temperature (Tc) as a function of annealing temperature at several pressures and by x‐ray determinations on the new phase, both retained at one atmosphere and at high pressure and temperature. The higher Tc for InSb‐III (Tc = 4.1°±0.1°K) and the x‐ray results lead to the conclusion that InSb‐III is a new phase different from the orthorhombic phase (Tc = 3.5°K).

Quenchable effects of high pressures and temperatures on the cubic monoxide of titanium

Abstract Changes in lattice parameter, density, number of vacancies and several transport properties of cubic TiO X , where 0.85 ≤ x ≤ 1.25, result from quenching under pressures of 50–60 kbar from annealing temperatures of 1100–1800°C. The superconducting transition temperature (T C ) increases linearly with oxygen content to a maximum of 2.0°K at x = 1.24 when ∼ 18% of the vacancies become filled during the pressure treatment.

Pressure Dependence of the Alpha-Beta Transition Temperature in Silver Selenide

The pressure dependence of the α-β transition temperature in Ag2Se was determined by observing the temperature at which the sharp change in resistivity occurs when Ag2Se is transformed from the low-temperature orthorhombic to the high temperature body-centered-cubic form. The transition temperature increased from 133�C at 1 atmosphere to 298�C at 47 kilobars. The value of ΔHt, the heat of transformation, of 2.19 kcal/mol measured calorimetrically agreed well with the value calculated from dT/dP of the transition.

Polymorphism in selenospinels—A high pressure phase of CdCr2Se4☆

Abstract The selenospinel, CdCr 2 Se 4 , has been transformed under high-pressure and temperature to a new structure with monoclinic symmetry related to the defect-NiAs structure and with the lattice parameters: a = 14.62A, b = 6.90A, c = 11.45A, and β = 91.0°. This is consistent with the spinel-to-monoclinic transformations found for the thiospinels, FeCr 2 S 4 , CoCr 2 S 4 , and MnCr 2 S 4 . The high-pressure phase is retained indefinitely at atmospheric pressure and room temperature but retransforms at 125C. The pressure-temperature boundary between the phases has a slope of −15.2°/kbar over the temperature range of 400–750C. Under pressure, the structural change is accompanied by a change from semiconducting to metallic electrical behavior with a drop in resistance from 5 × 10 2 –5.5 × 10 −2 ohms. The magnetic moment at 4.2K decreased from ∼5.6μ B for the spinel phase, which orders ferromagnetically, to ∼0.035μ B for the monoclinic phase, which has weak antiferromagnetic ordering.

Resistivity, magnetoresistance, and hall effect studies in VOx(0.82 ⩽ x ⩽ 1.0)☆☆☆

Abstract Resistivity (ϱ), magnetoresistance ( Δϱ ϱ 0 ), and Hall coefficient (R) measurements were carried out on annealed, polycrystalline, single phase VOx(0.82 ⩽ x ⩽ 1.0) samples at T = 4.2, 77, 300°K. These samples did not undergo a semiconductor-metal transition; they had room temperature resistivities in the range 10−3 > ϱ > 10−4 Ω cm, small negative values of dϱ dT , small Hall coefficients R ∼ 5 × 10−4 cm3/C, and positive values of Δϱ ϱ 0 at 4.2°K. An overlapping band structure model is proposed to explain these and comparable observations in the literature.