An apparent transition between active and nonactive secondhyphen;harmonic generation (SHG) has been discovered in the NaNb3O8solid solutions with the tetragonal tungsten bronze structure. No SHG was detected in 0.35Na2O:Nb2O5solid solution crystal or its powder. Nevertheless, powder SHG with a magnitude comparable to KH2PO4was observed when a small amount of Nb2O5was added to the powder ground from the crystal and sintered again. Microcracks and ferroelectric domain boundaries have been observed in the crystal using transmission electron microscopy. The only difference between the lattice images of SHG active powder and nonhyphen;SHG active powder is the absence of microcracks and ferroelectric domain boundaries in the SHG active powder. Dielectric constant of the 0.35Na2O:Nb2O5crystal is about 300 and dgr; is 0.003 for frequency from 120 kHz to 12 MHz.
展开▼
