PIEZOELECTRICALLY STIMULATED DIELECTRIC-DISPERSION IN KAP SINGLE-CRYSTALS

The frequency response of the dielectric constant (epsilon(r)), the lo ss tangent (tan delta) and impedance Z of potassium acid phthalate (KA P) single crystals, monitored along the polar axis, exhibit strong res onances in the frequency range 50-200 kHz, depending on the dimensions of the sample. The observed resonance effect, which is strongly depen dent on the geometric shape and size of the sample, is attributed to i ts piezoelectric nature. The resonance peak positions have been monito red as a function of both temperature and uniaxial pressure. The stiff ness coefficient (C), computed based on the resonance data, is found t o decrease with increasing temperature and increase with increasing pr essure. The electro-mechanical coupling coefficient (k), obtained by r esonance-anti-resonance method, has also been found to increase with r ise in temperature. The epsilon(r) behaviour along the polar axis, as a function of temperature is consistent with that of k. The preliminar y results on the influence, of partial replacement of K+ ions in the K AP crystal by Cs+ and Li+ ions, on the observed piezoelectric resonanc e effects are also included.