Temperature Dependence of Parametric Phenomenon in Airborne Ultrasound for Temperature Measurement

Abstract

In this detailed study we have reported on single-crystal and polycrystalline phases of V 1+x S 2 ; 0.10 < x < 0.25, prepared using excess sulfur in a sealed quartz tube and investigated their structural, transport and magnetic properties. The crystal flakes have trigonal symmetry with 2c and incommensurate >2( √ 3)a superlattice ordering in the a-b plane. As-grown flakes showed complex irreversible behaviour in resistivity on cycling to low temperatures, related to the metastability of the structure. The annealing of the crystal flakes and addition of 5-10% Al stabilizes the superstructure. We observe an anomalous contribution to the resistance of these crystal flakes with a maximum around 100-150 K. The contribution is more pronounced for betterordered phases. The magnetic susceptibility and thermopower values of these compounds are large and vary smoothly on cooling around this temperature interval. The polycrystalline phase, obtained at a higher temperature, on the other hand, showed absence of superlattice distortions and gave a smooth behaviour in its resistance, but with a large T 2 -contribution. The structural and electronic properties of different phases are discussed in terms of disorder among the interstitial V atoms and the effect of in-plane vacancies on the chargedensity-wave instability in these and similar compounds.

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