Origin of dielectric loss in Ba(Co_1/3Nb_2/3)O₃ microwave ceramics

Abstract

The microwave dielectric loss of stoichiometric and non-stoichiometric Ba (Co 1/3 Nb 2/3 )O 3 ceramics have been measured from 2 to 300 K in magnetic fields ranging from 0 to 5 T using a dielectric resonator (DR) technique. The microwave absorption from spin excitations of unpaired d-electrons in exchange coupled Co 2+ ions dominate the loss of the Ba(Co 1/3 Nb 2/3 )O 3 ceramics at cryogenic temperatures. Two peaks in the loss tangent (tan d) vs temperature relation from a distinctly different origin occur at 25-30 K and 90 K, which increase in magnitude with increasing Co content in the bulk dielectric samples. Evidence that these peaks result from polaron conduction from hopping between Co 2+ and Co 3+ ions includes (i) the peak's observed temperature range; (ii) the decrease in peak intensity of approximately a factor of two in a large applied magnetic fields (5 T); and (iii) a strong correlation between the peak's magnitude and both the fraction of the minority Co 3+ in the dominant Co 2+ matrix and D.C. conductivity at elevated temperatures. A magnetic-field independent high temperature peak with a maximum at 250 K dominates the room temperature microwave loss whose magnitude correlates with those of the low temperature peaks. This suggests that the defects responsible for carrier conduction play an important role in establishing the loss tangent at room temperature. K E Y W O R D Scomplex perovskite, dielectric loss, dipole relaxation, microwave resonator, point defect

Development of magnetically switchable high permittivity microwave dielectrics using La(Al1‐xFex)O3

“…These peaks can be fit to the Debye formula (),where τ is the relaxation time, T is the temperature, k B is the Boltzmann constant, ω is the angular frequency, ε 0 is the vacuum permittivity of free space, ε r is the relative permittivity, τ 0 is the relaxation time, η is the field correction factor on the order of one, N d is the defect concentration, P is the dipole's moment, and W is the activation energy. The intensity of the peaks above the background at ∼40 K, ∼75 K, and ∼215 K have little or no magnetic field dependence 22 …”

Influences of Mg and Mn doping on structure, B-site ordering and microwave dielectric properties of Ba(Co1/3Nb2/3)O3 ceramics

“…As shown, they are of relatively homogeneous composition. It is believed that abnormal grain growth is attributed to large grain annexation of small grains, which results from the appearance of vacancies induced by the evaporation of CoO or the change of the valence of Co or Mn [12,13]. It is well known that atom diffusion can be accelerated by vacancies that provide fast diffusion channel for mass.…”

“…Li et al [12] have demonstrated that microwave loss due to the presence of P-type bulk phase is associated with the mixed presence of Co 2+ and Co 3+ on the B-site lattice. Sayyadi-Shahraki et al [13] further verified that polaron hopping between Co 2+ and Co 3+ cations also contributes to the dielectric loss in Ba(Co 1/3 Nb 2/3 )O 3 at cryogenic temperatures. It is well known that the excellent microwave properties of BCN complex perovskite ceramics are related to pores, secondary phases, impurities, grain boundaries and B-site 1:2 ordering [14 -16].…”

Perovskite synthesis, properties and their related biochemical and industrial application

“…One of the environmental friendly photoluminescence (PL) is BaZrO 3 which emits light in the visible region and prepared easily at low cost (Di et al, 2018, Yagi, 2009). The property of PL makes it promising for applications such as; scintillators, solid state lightning, field emission displays, green photocatalyst and plasma displays (Sayyadi-Shahraki et al, 2017).…”