Effects of La 2O 3 additions on properties of Ba 0.6Sr 0.4TiO 3–MgO ceramics for phase shifter applications

Abstract

Influence of La 2O 3 additions on the microwave dielectric properties of Ba 0.6Sr 0.4TiO 3 (BST) mixed with magnesium oxide ( w = 60 % ) composites was investigated. With increasing quantities of lanthanum oxide x (wt%), the lattice constant of BST–MgO material decreases to a minimum at x = 0.4 and then increases up to a maximum at x = 1.0. The XRD patterns analysis reveal that the solubility of MgO in BST is influenced by the amount of La 2O 3 doping. SEM observations show that the BST grain sizes decrease with increasing amounts of La 2O 3. The dielectric properties of BST–MgO–La 2O 3 indicate that La 2O 3 additives shift the Curie point towards lower temperatures. Optimum doping amount of La 2O 3 can reduce the high frequency loss tangents of BST–MgO compound which also can ensure the moderate dielectric constant and tunability. Excessive doping of La 2O 3 tends to significantly lower dielectric constant and deteriorate tunability. When the doping amount of La 2O 3 is 0.2 wt%, BST–MgO composite has the following properties: dielectric constant = 94.05, tan δ = 0.012 (at 2.853 GHz) and the dielectric constant tunability = 16.26% (under electric field 3.57 kV/mm), which is suitable for ferroelectric phase shifter.