Structural, optical and dielectric studies on K_1‐x(NH₄)_xH₂PO₄ mixed crystals grown from z‐cut seeds

Abstract

Mixed crystals of K 1-x (NH 4 ) x H 2 PO 4 (KADP) were grown from KDP (KH 2 PO 4 ) dominated mixed solutions with varying molar proportion of ADP (NH 4 H 2 PO 4 ) addition. It was found that, as the increase of ADP molar concentration, the growth rate along z-axis of KADP crystal decreased rapidly. The structure of KADP crystals was investigated by powder XRD and the lattice parameter was calculated. The results showed that the lattice parameter c of KADP crystal increased with the molar concentration of ADP. The optical homogeneity of grown KADP crystals was determined with a differential phase-shifting interferometry. Frequency dependences of the dielectric constant and dielectric loss of KADP crystals were measured at room temperature (290 K). The dielectric constants of KADP crystals were almost invariant with the increase of frequency. In the region of 10 2 -10 4 Hz, the values of the dielectric loss reduced with the increase of frequency. The piezo-resonance coupling effect still exists in KADP crystals at room temperature, but shifted to low frequency band.

Piezoelectric Resonance in KH2PO4 Type Crystals Revisited

“…The ultimate goal of the present studies will be to generalize the obtained expression for the dynamic permittivity to the case of the Rb 1−x (NH 4 ) x PO 4 type proton glasses, in order to explore their dynamic dielectric response. It is known [9,10] that, just like their pure constituents, these mixed systems are piezoelectric, and their dynamic dielectric permittivity has a piezoelectric resonance dispersion. As our preliminary calculations show, the experimentally obtained resonant frequencies of such mixed crystals [11] are well described by the obtained here expression for the resonant frequencies, provided that the corresponding elastic constant c E 66 of such a system is known.…”

“…In our previous consideration [1] this condition was fulfilled at the corners of the crystal plate only, but not along all its edges. Substituting (10) into the constitutive relations, we obtain the explicit boundary conditions for the strains in the following form…”