我们利用激光分子束外延设备(L-MBE)在MgO上外延生长了一系列BaNbxTi1-xO3(0＜x≤0.5)薄膜.X射线和Raman测量显示薄膜随Nb掺杂量的增加从四方相转变为立方相.同时电学测量表明,薄膜的导电类型从半导体转变为金属.室温电阻率随掺杂量单调下降,变化范围从101 to 10-4Ω.cm.薄膜的电阻-温度曲线可以利用小极化子模型很好的拟合.这说明薄膜内的载流子主要是极化子.光电子能谱显示在BaTiO3的带隙中存在局域态,进一步说明薄膜内的载流子为极化子.

Thin films ofBaNb_xTi_1-xO₃ (0＜x≤0.5) were epitaxially grown onMgO substrates by laser molecular beam epitaxy (L-MBE). The thin films undergo tetragonalto cubic and semiconductor to metal transitions with Nb concentrations as shown by thex-ray diffraction, Raman spectroscopy and electrical resistivity measurements. Roomtemperature resistivities are found to decrease monotonously with increasing Nbconcentration and range from 101 to 10-4 Ω.cm. The fact that the temperature dependence of resistivity of thethin films can be fitted well using small polaron model reveals the polaronic nature ofthe charge carriers in the thin films. This conclusion is further confirmed by theexistence of localized states within the band gap of the BaTiO3 as revealed by thesynchrotron radiation-based ultraviolet photoelectron spectroscopy.