Grain size engineered 0.95MgTiO₃–0.05CaTiO₃ ceramics with excellent microwave dielectric properties and prominent mechanical performance

Abstract

Microwave communication systems are being developed with the goal to achieve miniaturization and high reliability. There are urgent requirements for microwave dielectric materials to exhibit low sintering temperatures, excellent microwave dielectric properties, and prominent mechanical performance. However, simultaneously achieving these requirements is a significant challenge. These concerns have been addressed in the uniform ultrafine-grained 0.95MgTiO 3 -0.05CaTiO 3 ceramics with an average grain size of ~0.6 µm via a grain size engineering strategy. Interestingly, the sintering temperature in the unique two-step sintering method of 1250℃/1 min and 1130℃/10 h is much lower (200-300℃) than that obtained in the conventional sintering method reported previously (1400-1450℃). Excellent dielectric properties are achieved, with relative permittivity ε r = 20.11, quality factor Q × f = 68 613 GHz, and temperature coefficient of resonant frequency τ f = 1.81 ppm/℃. The bending strength f , Vickers hardness H v , and elastic modulus E reach up to 212.4 MPa, 10.1 GPa, and 200.7 GPa, respectively. These values are significantly enhanced over those of samples obtained via the conventional sintering method with an average grain size of ~2.5 µm. For the first time, uniform ultrafine-grained microwave dielectric materials with excellent microwave dielectric properties and prominent mechanical performance were synthesized. This work provides a guideline for developing other high-performance microwave dielectric materials and makes a significant contribution to the miniaturization and high reliability of microwave dielectric devices.

MgTiO3–Ca1−xSm2x/3TiO3 (x = 0.2–0.5) microwave dielectric composites with greatly improved temperature stability

“…The results show that adopting suitable constituent phases with low associated | b 2 | and |$$\overline {\frac{{d{\tau _{f,S}}}}{{dT}}} $$| is an effective strategy to greatly improve the temperature stability of microwave dielectric composites with near‐zero average τ f and, therefore, shed light on the development of new temperature‐stable microwave dielectric composites. Furthermore, it is well known that MgTiO 3 –CaTiO 3 composite with near‐zero τ f,H and ε r of ∼21 is one of the most important commercial microwave dielectric ceramics and widely used as a K21 material 5,14–18 . The present work not only greatly improves the temperature stability of MgTiO 3 ‐based composites, but also increases ε r up to 27.1, and, therefore, may broaden their application.…”

“…Furthermore, it is well known that MgTiO 3 -CaTiO 3 composite with near-zero τ f,H and ε r of ∼21 is one of the most important commercial microwave dielectric ceramics and widely used as a K21 material. 5,[14][15][16][17][18] The present work not only greatly improves the temperature stability of MgTiO 3based composites, but also increases ε r up to 27.1, and, therefore, may broaden their application. Considering the traditional application of MgTiO 3 -based composites as a K21 material, it is also an important issue to maintain the ε r of ∼21 and high Qf value when improving the temperature stability.…”

“…13 As one of the most important commercial microwave dielectric ceramics, MgTiO 3 -CaTiO 3 composite is a popular research subject due to its good microwave dielectric properties, low cost, and excellent processing compatibility. [14][15][16][17][18] However, the τ f of MgTiO 3 -CaTiO 3 composite shows severe temperature dependence, although it was not reported until very recently. 5,12 The average τ f between 20 and 80 • C of 0.93MgTiO 3 -0.07CaTiO 3 composite is as low as 0.7 ppm/ • C, although f 0 first increases and then decreases with increasing temperature from −40 to 80 • C, and τ f decreases significantly from 19.2 to −5.5 ppm/ • C. 5 Obviously, the near-zero average τ f of 0.93MgTiO 3 -0.07CaTiO 3 composite determined using Equation ( 1) or (2) conceals its real temperature instability and strong nonlinear change of f 0 with temperature, and the temperature dependence of τ f should be reduced to improve the temperature stability of the composite for practical application.…”

“…More interestingly, it has been reported that the temperature dependence of τ f of randomly distributed composites and layered ceramics with near‐zero average τ f is more severe 5,6,10–12 and theoretically deduced to be common in the composites consisting of two phases with τ f of opposite signs 13 . As one of the most important commercial microwave dielectric ceramics, MgTiO 3 –CaTiO 3 composite is a popular research subject due to its good microwave dielectric properties, low cost, and excellent processing compatibility 14–18 . However, the τ f of MgTiO 3 –CaTiO 3 composite shows severe temperature dependence, although it was not reported until very recently 5,12 .…”

Effect of A-site modification on structural and microwave dielectric properties of calcium titanate

“…Two traditional techniques for dielectric ceramic modification with desired features are known: one is to produce a new dielectric ceramic material, and the other is to make a composite utilizing two or more dielectric materials with characteristic compensation. The most common strategy is to combine two or more chemicals with negative and positiveτ f values to achieve nearly equal zero τ f values [6,[9][10][11][12]. For example, 0.95MgTiO3 -0.05CaTiO3 ceramic shows (ε r ) ∼21, (Q × f) ∼56,000 GHz at 7 GHz and τ f ∼ 0 ppm/°C [11].…”