Electron Spin Resonance of Cu2+ Ion in Ferroelectric KDP Crystals

The electron spin resonance absorption of Cu 2+ ion doped in KDP single crystals were studied both in paraelectric and ferroelectric phases. There are two kinds of Cu 2+ sites in the crystals. It is inferred from the angular dependence of the ESR spectrum that one site is the potassium lattice site for which one of the eight nearest protons is missing, and the other is the potassium lattice site with which a potassium vacancy is associated at one of the nearest sites. The intensity of the ESR absorption abruptly changed when passing through the Curie temperature. This is accounted for as being caused by the abrupt change of the dielectric constant for microwave frequency. The effect of the application of electric field on the ESR spectrum was studied in the ferroelectric phase. The direct evidence for domain switching is obtained by the reversal of the polarity of the field.