Feng Duan

Ferroelectric crystals with periodic laminar domains as the micron superlattices for optic acoustic processes

Abstract The excitation and propagation of high frequency ultrasonic waves by the micron superlattices is cited as an example, the experimental results are compared with theoretical predictions. LiNbO3 and LiTaO3 crystals with periodic laminar domains with periods about several microns and several ten microns have been fabricated by Czochralski method of crystal growth with doped melts. These may be considered as the micron superlattices for optic and acoustic wave processes involving 3rd. rank tensor coefficients which change sign across the domain walls.

A study of screw dislocations in gadolinium gallium garnet and yttrium aluminium garnet crystals by birefringence topography

Abstract Birefringence images of screw dislocations in gadolinium gallium garnet (GGG) and yttrium aluminium garnet (YAG) crystals have been studied in detail and birefringence images of screw dislocations viewed end-on have been observed for the first time. The one-to-one correspondence between birefringence images of screw dislocations viewed end-on and those viewed from the side is demonstrated. The contours of equal intensity for birefringence images of screw dislocation viewed end-on in GGG and YAG crystals are calculated and presented.

Ferroelectric crystals with periodic laminar domains

Abstract This paper reviews our researches on the growth, the characterization and the physical properties of ferroelectric crystals with periodic laminar domains. The growth of LiNbO3 and LiTaO3 crystals with periodic laminar domains has been achieved in Czochralski growth system. The melt was doped with solutes such as yttrium, indium or chromium. Either eccentric rotations or applying electric current pulses with reversed polarities was used to induce the growth striations in the growing crystals. Two kinds of domain walls, the smooth vs. the rough have been found with electron microscopic observations. The determination of solute concentration variation along the growth axis shows that there are sharp minima and broad maxima which correspond to the smooth and the rough domain walls. The mechanism for the formation of periodic laminar domains has been discussed. Components of a 3rd rank tensor such as nonlinear optical or piezoelectric coefficient may change sign across a ferroelectric domain wall. For...

Electron-microscopy studies of pure and doped electrooptic PLZT ceramics

Abstract Data on chemical composition and spatial fluctuations thereof as well as fracture mode behaviour of pure and doped PLZT ceramics have been obtained.