钨青铜型Ca_(0.28)Ba_(0.72)Nb_2O_6单晶中铁电畴结构及其演变的透射电镜研究

A TEM Study of 180° Ferroelectric Domains and Their Evolution in Ca_(0.28)Ba_(0.72)Nb_2O_6 Single Crystals of Tungsten Bronzes Structure

用透射电镜研究了CBN-28单晶中的180°畴结构及其演变.发现其中存在高密度的180°铁电畴,这些畴呈长钉状或棒状,沿c轴走向,直径约50～500nm.观察到电子束辐照诱致的畴壁运动.原位加热观察表明,升温至220℃左右,开始出现许多直径仅几纳米的细条状微畴;温度再上升时这种细条状畴逐渐增多.在282℃时所有畴衬度消失.这种零场自发极化的宏畴→微畴转变对应于在铁电相变点Tc附近的正常→弛豫铁电体转变.温度降至196℃以下时,形成了直径约10～50nm稳定的条状畴.

A high density of 180° ferroelectric domains in Ca_ 0.28 Ba_ 0.72 Nb_2O_6 ℃BN-28) single crystals has been observed with the aid of transmission electron microscopy. The 180° domains appear predominantly spike-shaped or rod-shaped along the polar axis (c-axis) and have a typical diameter of 50～500 nm. The motion of domain walls was occasionally induced by electron beam irradiation. In-situ observations during heating were carried out in an electron microscope. Macrodomains-to-microdomains transition, corres...