Microstructure and Microwave Dielectric Properties of Ba3.75Nd9.5Ti18−z (Mg1/3Nb2/3) z O54 Ceramics

Abstract

The effects of magnesium and niobium substitution for titanium on the microwave dielectric properties of Ba 3.75 Nd 9.5 Ti 18Àz (Mg 1/3 Nb 2/3 ) z O 54 (0 £ z £ 3) ceramics were studied. The temperature coefficient of resonant frequency (s f ) decreased from about +60 ppm/°C to +17 ppm/°C when z £ 1. Excellent quality factor (Qf = 7300 GHz) as well as high dielectric constant (e r = 80.96) were obtained. For z ‡ 1.5, Nd 2 (Ti,Mg,Nb) 2 O 7 secondary phase appeared which would obviously influence the microwave dielectric properties. As z varied from 0 to 3, matrix grain size degraded which would obviously deteriorate the microwave dielectric properties by conducting more pores, especially the Qf value. The s f value was found to be related to b-site bond valence (V B-O ) and unit cell volume (V m ). Average ionic polarizability (a D ) and relative density evidently influenced the dielectric constant.

A novel formula for the quality factor calculation for the multiphase microwave dielectric ceramic mixtures

“…Microwave dielectric ceramics have been widely utilized in microwave applications, for example, resonators, because of their high dielectric constant (ε r ) and high quality factor (Q) [1][2][3][4][5][6]. Dielectric constant of ε r can result in the size of devices being ε r 1/2 times smaller; high quality factor (Q), which is approximately the reciprocal of the dielectric loss (tanı), represents low energy loss and precise frequency selection [1,2,4].…”

“…Dielectric constant of ε r can result in the size of devices being ε r 1/2 times smaller; high quality factor (Q), which is approximately the reciprocal of the dielectric loss (tanı), represents low energy loss and precise frequency selection [1,2,4].…”

PHASE EVOLUTION AND MICROWAVE DIELECTRIC PROPERTIES OF Ca0.61Nd0.26Ti1-x (Al1/2Nb1/2)xO₃ CERAMICS (0 ≤ x ≤ 0.2)

“…The quality factor and temperature coefficient of resonant frequency both declined as well. For 0 ≤ x ≤ 0.1, though the grain size decreased tremendously, relative density of specimens were higher than 95 %, we concluded that the dielectric constant was controlled by average ionic polarizability, which has been clarified in [2,15,16]. For the decreasing quality factor, it probably was because of the decreasing grain size, in other words more grain boundaries in unit volume [17].…”

“…Microwave dielectric ceramics have been widely utilized in wireless communication systems [1], such as RFID devices [2,3], Radar [1], and mobile telephone [1]. Microwave dielectric materials in these applications are guided by the high relative permittivity to minimize the device size [2,3], the high Q value to optimize the signal selection, and near zero temperature coefficients at resonant frequency for a stable work frequency 1 .…”

“…Microwave dielectric materials in these applications are guided by the high relative permittivity to minimize the device size [2,3], the high Q value to optimize the signal selection, and near zero temperature coefficients at resonant frequency for a stable work frequency 1 . This guidance gives rise to wide researches on high dielectric constant ceramics for their impractical τ f values.…”