N. Victor Jaya

Structural studies of CuAlSe2 and CuAlS2 chalcopyrites at high pressures

Abstract The ternary chalcopyrite compounds CuAlSe 2 and CuAlS 2 were studied up to 14.8 GPa in a diamond anvil cell by energy dispersive X-ray diffraction (EDXRD). The powder X-ray diffraction data at high pressure show that CuAlSe 2 undergoes a pressure-induced structural phase transition around 12.5 GPa from the chalcopyrite structure to NaCl type structure. CuAlS 2 exhibits structural stability up to 14.8 GPa. The pressure-induced structural phase transition observed in the EDXRD experiments is consistent with the theoretical total energy calculations. The results are consistent with the conclusions of a recent high-pressure Raman study reported for these compounds.

Pressure induced structural phase transition in YBa2Cu3O7

Abstract High pressure X-ray diffraction studies and electrical resistivity measurements have been performed on high T c superconductor YBa 2 Cu 3 O 7 up to 110 kbar at room temperature. X-ray results indicate an orthorhombic to tetragonal phase transition above 70 kbar. The transition is reversible. Electrical measurements also show a decrease in resistivity up to 70 kbar and then an increase.

Design and performance of a belt-type high pressure, high temperature apparatus

A modified belt-type high pressure, high temperature apparatus without tungsten carbide has been designed and constructed based on the theory of multilayered pressure vessels. The calculated interferences seem to give adequate support for reaching a high pressure of 10 GPa and simultaneously temperatures up to 1400 °C. We estimate the highest pressure reached in our experiment to be ∼17 GPa in the sample region, based on the load versus pressure curve calibrated in bismuth, tin, and lead. Talc gaskets were used along with a tubular graphite furnace for high temperatures. This represents a relatively simple and inexpensive device for material synthesis and phase transformation studies.

MEASUREMENT OF THERMOELECTRIC POWER USING METAL OPPOSED ANVIL CELLS UP TO 100 KBAR

In this paper we describe the design of a simple Bridgman opposed anvil cell to measure the thermoelectric power of solids as a function of pressure up to 100 kbar. The anvils are made of EN‐24 alloy steel hardened to RC55.

Synthesis and high pressure studies of the semiconductor AgSbSe2

Abstract We have synthesised the ternary semiconducting compound AgSbSe 2 by fusing the constituent elements in a vacuum sealed quartz tube. High pressure resistivity studies were performed on the compound up to 8 GPa using the opposed anvil high pressure device (OAHPD) on employing four probe technique. Powder X-ray diffraction experiments were carried out up to 15 GPa using a Mao–Bell type Diamond Anvil Cell (DAC). The results show that the compound remains in the NaCl structure up to the experimental limit. The bulk modulus has been calculated to be 129 GPa.

Effect of Mn-Doping on Structural, Optical, and Dielectric Properties of SnO2 Nanoparticles by Coprecipitation Method

Pure and Mn-doped SnO2 nanoparticles are prepared by co-precipitation method. The structural analysis reveals the presence of tetragonal system of SnO2. Fourier transform infrared spectroscopy (FTIR) spectra of pure SnO2 show the occurrence of O-Sn-O vibrational mode at around 671 cm−1. It is observed that the wavenumber is shifted to lower region with the increase in Mn dopant concentration. As the Mn content is increased, a clear indication of red shift is observed in the UV-vis absorption spectra. From the scanning electron microscope (SEM) image, the surface morphology of the sample shows uniformly dispersed particles, which are spherical in shape. From dielectric studies, the dielectric constant suddenly drops to 0.5 × 106 Hz, and thereafter, it shows a constant behavior. Dielectric loss plot of the prepared samples exhibits a linear behavior at higher frequency region, which suggests the samples possess a lossless nature. The ac conductivity value drops linearly with the increase in dopant level. This is due to the particle size effect and screening effect caused by the impurities.

STRUCTURAL TRANSFORMATION IN PbS AND HgS NANOCRYSTALS UNDER HIGH PRESSURE

The phase transition induced by pressure in the PbS and HgS nanocrystals was studied by in situ high pressure X-ray powder diffraction measurements. PbS underwent a phase transition from B1-B16 at 7 GPa whereas no transition was observed in HgS up to 15 GPa. The transition remained unaltered on the release of pressure. The volume decreased with an increase in pressure. There is a shift in transition pressure towards the higher side when compared with the bulk materials.

Design and fabrication of a simple pneumatic loading attachment for diamond anvil cells

A simple pneumatic pressure attachment has been designed and fabricated for Mao–Bell and National Bureau of Standard type diamond anvil cells (DACs). The assembly can be fitted to the lever arm of the DAC for applying pressure on the diamonds and the pressure at the sample site has been calibrated against the gas dial using the equation of state of silver loaded in the DAC.

High Pressure Electrical Resistivity of Composition Controlled Nd-123 Based Bulk Material

High pressure electrical resistivity studies were carried out on the high temperature superconductor Nd1-xCaxBa2Cu3O7-δ for various calcium concentrations x=0.00, 0.03, 0.06 and 0.10 obtained by the solid-state reaction method. The electrical resistivity study was performed using the four-probe technique with a Bridgman opposed anvil device. All four samples show an initial drastic fall in electrical resistivity up to a pressure of around 3 GPa that remains almost constant up to 8 GPa.

Structural, optical and high pressure electrical resistivity studies of pure NiO and Cu-doped NiO nanoparticles

In this paper, pure NiO and Cu-doped NiO nanoparticles are prepared by co-precipitation method. The electrical resistivity measurements by applying high pressure on pure NiO and Cu-doped NiO nanoparticles were reported. The Bridgman anvil set up is used to measure high pressures up to 8 GPa. These measurements show that there is no phase transformation in the samples till the high pressure is reached. The samples show a rapid decrease in electrical resistivity up to 5 GPa and it remains constant beyond 5 GPa. The electrical resistivity and the transport activation energy of the samples under high pressure up to 8 GPa have been studied in the temperature range of 273–433 K using diamond anvil cell. The temperature versus electrical resistivity studies reveal that the samples behave like a semiconductor. The activation energies of the charge carriers depend on the size of the samples.