title: Direct observation of the microstructure and defects in KBe2BO3F2 crystals by TEM.
abstract: We apply for the first time transmission electron microscopy to the direct observation of the deep-UV nonlinear optical crystal KBe2BO3F2 (KBBF) grown using different methods. Two kinds of electron diffraction patterns were observed in the hydrothermally synthesized KBBF along the [120] direction, which resulted from the coexistence of two structures with space groups R32 and R3[combining macron]c. As a comparison, the flux grown KBBF crystals show uniform R32 structures. Furthermore we observed a twin boundary in flux KBBF which corresponds to the (21[combining macron]3)R32 crystallographic plane. Two structure models are proposed here for the twin boundary. These observations on the microstructure and defects were not disclosed in previous powder XRD and optical microscopy experiments and shed new light on the understanding of the structure and defects of KBBF crystals.
authors.affiliation: Beijing Center for Crystal Research and Development, Key Lab of Functional Crystals and Laser Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China. llj@mail.ipc.ac.cn.
authors.forename: Tao
authors.initials: T
authors.lastname: Xu
authors.forename: Lijuan
authors.initials: L
authors.lastname: Liu
authors.forename: Xiaoyang
authors.initials: X
authors.lastname: Wang
authors.forename: Chuangtian
authors.initials: C
authors.lastname: Chen
authors.forename: Haitao
authors.initials: H
authors.lastname: Zhou
authors.forename: Xiaoling
authors.initials: X
authors.lastname: He
authors.forename: Changlong
authors.initials: C
authors.lastname: Zhang
authors.forename: Junliang
authors.initials: J
authors.lastname: Sun