Preparation and characterization of La-doped Ba (1 − x) Sr xTiO 3 powders and thin films

Abstract

Ba (1 − x) Sr x TiO 3 powders with different Ba/Sr ratios ( x = 0.10, 0.25, 0.40, 0.55, 0.70) and La-doped Ba 0.9Sr 0.1TiO 3·yLa powders ( y = 0.002, 0.004, 0.006, 0.008, 0.010) have been prepared by sol–gel technology using dehydrated barium-acetate, strontium-carbonate, lanthanum-nitrate, and titanium-isopropoxide as raw materials. The experimental results show that the dielectric properties of Ba (1 − x )Sr x TiO 3 powders depend on the Ba/Sr ratios. When the Sr fraction is 0.10, the dielectric constant is relatively higher and the dielectric loss is relatively lower, which are more than 2000 and less than 2.0 × 10 − 2 at 1000 Hz, respectively, the most important is that this kind of powder has better frequency stability. La-doping can increase the dielectric constant distinctly, but the dielectric loss can also be increased. Their dielectric properties at 1.0 × 10 3 Hz are better than those at 1.0 × 10 5 Hz. At 1.0 × 10 3 Hz the dielectric constant is much higher, while the dielectric loss is much lower. The dielectric constant of different La-doping contents is nearly 3.5 × 10 4 and the dielectric loss is less than 0.20 when La fraction is 0.008. The La-doped BST sample also has better frequency stability, especially at high frequency. La-doped BST thin films are successfully deposited on mild steel substrates by using plasma spray system with suspension precursors of Ba 0.90Sr 0.10TiO 3·0.8La powders. The XRD patterns of Ba 0.90Sr 0.10TiO 3 and Ba 0.90Sr 0.10TiO 3·0.8La powders are almost the same. No new peaks appear after La-doping, but the peaks move slightly to a larger degree, which indicates that the element La has entered the lattice of the Ba 0.90Sr 0.10TiO 3 and has made the constant of the crystal cell reduce. The XRD pattern of the thin films is just like that of the Ba 0.90Sr 0.10TiO 3·0.8La powders except a peak corresponding to Fe substrate. The SEM results show that the thin films have a uniform and smooth surface. The morphology of cross-section shows a columnar grain structure indicating smooth surface and uniform thickness of the film. The thickness of the film is about 15 um. The thin films obtained are expected to be prospective material for applications in tunable microwave devices.