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The thermopower (TEP) and electrical resistance of stoichiometric Fe30& crystals have been measured up to pressures of 6 GPa over the temperature range of 80 -160 K. The resistance decreases markedly with increasing pressure below the Verwey transition temperature T& and Tv decreases linearly with increasing pressure. The magnitude of the TEP as well as the discontinuity at Ty decrease with increasing pressure. The thermopower of Fe30& shows an interesting upswing at low temperatures ( (100 K) which is afFected significantly by pressure.The eFect of pressure on the Verwey transition of Fe304 has been investigated by a few workers. Samara'obtained the values of the transition temperature, T", in natural single crystals from electrical resistivity measurements at different pressures and found the pressure derivative to be -4.8 K GPa ' up to 4.5 GPa. By keeping the temperature constant at 77 K, the Verwey transition was encountered at pressures between 8 and 10 GPa, suggesting that the transition should occur between 25 and 30 GPa at 0 K. Samara concluded that the observed decrease in T"with increasing pressure and the applicability of the locali. zed electron model for conduction below T"are consistent with the Mott-Wigner model for the transition. Schloessin and Govindarajan have reported a similar pressure coefficient up to 5.6 GPa in natural single crystals of Fe304. Kakudate, Mori, and Kino carried out electrical resistivity measurements on synthetic single crystals and obtained a pressure coefficient of T"of -2.7 K GPa ' up to 1.84 GPa. Clearly, there is room for a detailed study of the effect of pressure on electron transport properties, especially the thermopower of stoichiometric crystals of Fe304 through the Verwey transition. Recent studies ' have shown that the Verwey transition is very sensitive to stoichiometry. In this communication, we report a study of the thermoelectric power (TEP) of stoichiometric synthetic Fe304 crystals up to pressures of 5 GPa over the temperature range of 80 to 160 K. We have also carried out resistance measurements on the stoichiometric crystals under the same conditions.Fe3O4 single crystals, grown by the skull melting procedure, were annealed around 1000 K in a controlled CO2/CO atmosphere. A piece of the crystal measuring approximately 1 X 1 XO. 5 mm was cut polished on a rotating wheel with diamond paste down to 0.15 mm thickness. TEP measurements under pressure were made using tungsten carbide anvils (without binding rings) powered by a 100-ton hydraulic ram. In order to maintain the integrity of the crystal upon pressurization, the crystal piece was set at the center of a pyrophyllite gasket with a mixture of talc and epoxy. The epoxy was allowed to set and the gasket-sample assembly formed the middle gasket in a stake of three gaskets. The top and the bottom gaskets with talk discs at the center contained copper leads and chromel-alumel thermojunctions. A Dewar surrounded the anvils. By controlling the rate of How of nitrogen vapor through the Dewar, the temperature c...

Novel CuBi2O4 nanocrystals incorporated in the polyaniline matrix utilized for the fabrication of a flexible and bio-compatible device for the detection of low-intensity photons by using a photomultiplication type photodetector.

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The electrical transport properties of the ladder polymer BBL in film forms were studied as a function of pressure. The sample resistance was monitored in two different configurations, perpendicular (transverse) and parallel (surface) configurations. The results reveal a significant difference in the pressure dependence of resistance between the two configurations. Photocurrent as a function of photon energy was measured to determine changes in the electronic structure in the pressurized and released samples. Results indicate an absence of shifts in the band edge but higher photocurrent efficiencies were observed for the films.