High-frequency characteristics of (Ba,Sr)TiO3 tunable ceramics with various additives intended

Bulk ferroelectric microwave devices based on (Ba,Sr)TiO3 (BST) ceramics were developed for the accelerator physics experiments with the Dielectric Loaded Accelerators (DLA). The DLA concept is a promising one to provide a development of high gradient accelerating structures. The BST ceramics have most acceptable dielectric constant, tunability, dielectric loss factor and electric durability to be used as a material for the tunable layer of the DLA accelerating structure. Various characteristics of BST ceramics with magnesium additives-BSM and the ceramics with lanthanoid elements-BSL designed to improve a quality of the BST compounds were studied. The capacitance-voltage C(V) and the current-voltage I(V) characteristics as well as the temperature dependencies of the layered capacitors were measured at f = 1 MHz. The BSM and BSL ceramics showed similar tunability coefficient that was about 10% at electrical field of 2 V/mu m. BSM samples were distinguished by lower dielectric losses and BSL samples found to have lower hysteresis of C(V) characteristics and higher stability. The results of microwave (MW) study showed good conformity of epsilon, tan delta and tunability coefficient at 1 MHz frequency band. The resonance frequency shift measured was 10% as well as at bias field of 2 V/mu m at the 10-13 GHz frequencies range.