A new experimental method of investigating phase transitions of solids, photothermal radiometry, is described. The effects of modulation frequency, laser intensity, and heating-cooling rates on the first-order semiconductor-to-metal phase transition of a microcystalline vanadium dioxide sample have been studied. The PTR signal increases with temperature in both phases, and a negative peak occurs at the phase transition. The intensity of signal is inversely proportional to the square root of frequency at laser-beam chopping frequencies lower than 100 Hz, indicating that the sample is thermally thick, and the signal is controlled by the thermal conductivity and the heat capacity and is independent of the optical properties of the material.
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