Open Access Research Article Issue
A novel Na1−xKxTaO3 perovskite microwave dielectric ceramic with high permittivity and high positive temperature coefficient
Journal of Advanced Ceramics 2023, 12 (11): 2053-2061
Published: 29 November 2023

A novel Na1−xKxTaO3 (x = 0, 0.025, 0.05, 0.075, 0.1, and 0.15) ceramic with high permittivity and high positive temperature coefficient was synthesized via the conventional solid-state method. All samples were determined to be pure phase orthorhombic NaTaO3 structure of space group Pmcn, and larger grain and lower porosity were observed after adding an appropriate amount of K+ ions. The Q × f value is majored by the packing fraction and grain size, while the value of τf is influenced by Ta–O bond valence. The Na0.95K0.05TaO3 ceramic possesses excellent dielectric properties of εr = 164.29, Q × f = 9091 GHz (f = 3.15 GHz), tanδ = 3.46×10–4, τf = +809.52 ppm/℃, sintered at 1550 ℃. Compared with NaTaO3 ceramics, the Na1−xKxTaO3 ceramics prepared in this study demonstrate higher dielectric constants and higher positive temperature coefficients, which are promising for device miniaturization and τf compensators.

Open Access Research Article Issue
Structure, far-infrared spectroscopy, microwave dielectric properties, and improved low-temperature sintering characteristics of tri-rutile Mg0.5Ti0.5TaO4 ceramics
Journal of Advanced Ceramics 2023, 12 (2): 296-308
Published: 10 January 2023

In this study, tri-rutile type Mg0.5Ti0.5TaO4 ceramics were synthesized, where the structure–property relationship, especially the structural configuration and intrinsic dielectric origin of Mg0.5Ti0.5TaO4 ceramics, and the low-firing characteristics were studied. It is found that the tri-rutile structural type is unambiguously identified through the Rietveld refinement analysis, the selected area electron diffraction (SAED), and the high-resolution transmission electron microscopy (HRTEM) along the [110] zone axis. With the increase in sintering temperature, the densification and uniformity of crystal growth play important roles in regulating the microwave dielectric properties of Mg0.5Ti0.5TaO4 ceramics. Intrinsically, theoretical dielectric properties calculated by the far-infrared reflective spectra approached the experimental values, indicating the importance of structural features to dielectric properties. Furthermore, a glass additive with high matching relevance with ceramics has been developed to decrease the high sintering temperature of Mg0.5Ti0.5TaO4 ceramics, where 2–4 wt% Li2O–MgO–ZnO–B2O3–SiO2 (LMZBS) glass frit was adopted to reduce the suitable temperature from 1275 to 1050 ℃ without significantly deteriorating the microwave dielectric characteristics. Specifically, Mg0.5Ti0.5TaO4 ceramics containing 2 wt% glass addition sintered at 1050 ℃ for 4 h possess excellent microwave dielectric properties: dielectric constant (εr) = 44.3, quality factor multiplied by resonant frequency (Q×f) = 23,820 GHz (f = 6.2 GHz), and the temperature coefficient of resonant frequency (τf) = 123.2 ppm/℃.

Open Access Review Issue
The latest process and challenges of microwave dielectric ceramics based on pseudo phase diagrams
Journal of Advanced Ceramics 2021, 10 (5): 885-932
Published: 11 October 2021

The explosive process of 5G communication evokes the urgent demand of miniaturized and integrated dielectric ceramics filter. It is a pressing need to advance the development of dielectric ceramics utilization of emerging technology to design new materials and understand the polarization mechanism. This review provides the summary of the study of microwave dielectric ceramics (MWDCs) sintered higher than 1000 ℃ from 2010 up to now, with the purpose of taking a broad and historical view of these ceramics and illustrating research directions. To date, researchers endeavor to explain the structure-property relationship of ceramics with multitude of approaches and design a new formula or strategy to obtain excellent microwave dielectric properties. There are variety of factors that impact the permittivity, dielectric loss, and temperature stability of dielectric materials, covering intrinsic and extrinsic factors. Many of these factors are often intertwined, which can complicate new dielectric material discovery and the mechanism investigation. Because of the various ceramics systems, pseudo phase diagram was used to classify the dielectric materials based on the composition. In this review, the ceramics were firstly divided into ternary systems, and then brief description of the experimental probes and complementary theoretical methods that have been used to discern the intrinsic polarization mechanisms and the origin of intrinsic loss was mentioned. Finally, some perspectives on the future outlook for high-temperature MWDCs were offered based on the synthesis method, characterization techniques, and significant theory developments.

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