Spontaneous unipolarity and anomalies of the dielectric and piezoelectric properties and electrical conductivity of initially heavily doped polydomain LiNb[O.sub.3]: Zn crystals

A significant spontaneous unipolarity in initially polydomain LiNb[O.sub.3]:Zn crystals doped in the range of "threshold" impurity concentrations (~4.5-4.7 mol %) has been revealed from high-temperature measurements and after high-temperature annealing under short circuit conditions. The effect of strong increase in the spontaneous unipolarity is accompanied by a pronounced low-frequency dielectric dispersion and abrupt anomalies in the temperature dependences of the electrical conductivity and dielectric permittivity. The piezoelectric coefficient [d.sub.333] increases to nearly maximum values available in the reference literature for nominally pure single-domain LiNb[O.sub.3] crystals.