Structures and Dielectric Properties of K and Mg Alternately Doped BST Films

Abstract

K and Mg alternately doped Ba_0.6Sr_0.4TiO₃ (BST) films denoted as K/Mg-BST and Mg/K-BST films have been prepared by improved sol-gel method, and their structures and dielectric properties have been studied. Pure, K doped and Mg doped BST films are also studied. X-ray diffraction reveals that all doped films show cubic perovskite structures, better crystallization and smaller average grain size than the pure BST film, K doping corresponds to weaker crystallization but larger grain size than other dopings, and Mg doping corresponds to the smallest grain size. K⁺ ions mainly substitute Sr²⁺ ions, while Mg²⁺ ions substitute Ti⁴⁺ ions, resulting in acceptor doping. Scanning electron microscopy shows that Mg doping causes the best surface structure, while K doping causes the worst one. K and Mg alternate doping results in lower dielectric loss than K doping and higher tunability than Mg doping, thus overcomes the drawbacks of K doping or Mg doping. K/Mg doping corresponds to the best combination of dielectric properties with loss of 1.17%, tunability of 32.5% at −20V and FOM of 23.1 at 100 kHz, thus is the most effective to achieve excellent dielectric properties for tunable microwave application.

Keywords:

• BST films
• K and Mg alternate doping
• combination of dielectric properties