Key Takeaways & Executive Findings
- •• A novel high-entropy ceramic (Mg0.5Zn0.5)0.4+xLi0.4(Ca0.5Sr0.5)0.4−xTiO3 was synthesized via solid-phase method, achieving near-zero τf (−8.6 ppm/°C) at x=0.35. • The ceramics exhibit excellent microwave dielectric properties: εr = 17.6, Q×f = 40900 GHz, making them promising for wireless communication. • The secondary phase Ca0.5Sr0.5TiO3 and [TiO6] octahedral distortion critically influence dielectric properties, providing a design strategy. • This work demonstrates that high-entropy engineering can effectively tailor temperature stability and performance of microwave dielectrics.
Abstract
A series of high-entropy ceramics with the nominal composition (Mg0.5Zn0.5)0.4+xLi0.4(Ca0.5Sr0.5)0.4−xTiO3 (0 ≤ x ≤ 0.4) has been successfully synthesized using the conventional solid-phase method. The (Mg0.5Zn0.5)0.4+xLi0.4(Ca0.5Sr0.5)0.4−xTiO3 ceramics are confirmed to be composed of the main phase (Zn,Mg,Li)TiO3 and the secondary phase Ca0.5Sr0.5TiO3 by X-ray diffractometer, Rietveld refinement, and X-ray spectroscopy analysis. The quality factor (Q×f) of the samples is inversely proportional to the content of the Ca0.5Sr0.5TiO3 phase, and it is influenced by the density. The secondary phase and molecular polarizability (αT) have a significant impact on the dielectric constant (εr) of the samples. Moreover, the temperature coefficient of resonant frequency (τf) of the samples is determined by the distortion of [TiO6] octahedra and the secondary phase. The results indicate that (Mg0.5Zn0.5)0.4+xLi0.4(Ca0.5Sr0.5)0.4−xTiO3 ceramics achieve ideal microwave dielectric properties (εr = 17.6, Q×f = 40900 GHz, τf = −8.6 ppm/°C) when x = 0.35. (Mg0.5Zn0.5)0.4+xLi0.4(Ca0.5Sr0.5)0.4−xTiO3 ceramics possess the potential for application in wireless communication, and a new approach has been provided to enhance the performance of microwave dielectric ceramics.
1. Introduction
Microwave dielectric ceramics are widely utilized in microwave resonators, filters, oscillators, phase shifters, and substrates [1]. Currently, the miniaturization, chip integration, and consolidation of microwave devices are key trends in development. The advancement of cutting-edge wireless communication technology, represented by 5th generation mobile communication technology (5G), has put forward higher and newer requirements for the performance of microwave dielectric ceramics. One of the keys focus in recent years has been the development of microwave dielectric ceramics with low loss, relatively high dielectric constants (εr, 20–100), and near-zero temperature coefficient of resonant frequency (τf ) [2–3].
“High-entropy” as a novel material design method, has greatly enriched the material system and also provided an avenue for high-performance dielectric materials required in wireless communication systems [4]. Lu et al. [5] proposed to combine body-centered cubic (BCC) and face-centered cubic (FCC) phases to form multiphase high-entropy alloys to obtain a significant increase in the overall performance of the materials. Currently, researchers classify high-entropy alloys into single-phase, two-phase, and multi-phase types based on their phase composition. The concept of “entropy engineering” involves designing materials by controlling configurational entropy [6]. The Gibbs free energy (G) is defined by the equation: G = H − TS, where H is enthalpy, T is temperature, and S is configurational entropy. In general, a system with the S greater than or equal to 1.5R (R denotes the molar gas constant with the value of 8.314 J·mol−1·K−1) is a high-entropy material [7]. Using high-entropy design strategies, several high-entropy ceramics with excellent performance were successfully prepared. (Mg0.2Ni0.2Zn0.2Co0.2Mn0.2)2SiO4 ceramic, produced by traditional solid-state methods, achieved excellent microwave dielectric properties (εr = 8.02, tangent of loss angle tan δ is 0.00051 at 14.5 GHz, and τf = −38.2 ppm/°C) [8]. A perovskite-type (La0.2Li0.2Ba0.2Sr0.2Ca0.2)TiO3 ceramic obtained a high dielectric constants (εr = 230) [9]. Li(Gd0.2Ho0.2Er0.2Yb0.2Lu0.2)GeO4 ceramic was synthesized and achieved a near-zero τf value (−2.9 ppm/°C) [10]. These results indicate that the high-entropy compositional could provide innovative approaches for improving the temperature stability and other properties of microwave dielectric ceramics.
Compared to MTiO3 (M = Mn, Ni, and Co), the ilmenite-structured MgTiO3 demonstrated exceptional microwave dielectric properties among low-loss ceramic materials [11]. However, a large negative τf value (τf = −50 ppm/°C) and a high sintering temperature (about 1450°C) limits the practical application of MgTiO3 (MT) [12–14]. Blending compounds with opposite τf value is one of effective methods to achieve near-zero τf.
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Xingyue Liao, Yuanming Lai, Huan Huang, Mingjun Xie, Weiping Gong, Yuanxun Li, Qian Liu, Chongsheng Wu, Jiao Han, Yiming Zeng (2025). Temperature-stabilized novel high-entropy microwave dielectric (Mg0.5Zn0.5)0.4+xLi0.4(Ca0.5Sr0.5)0.4−xTiO3 ceramics. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-024-3021-6
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Frequently Asked Questions
What are the key microwave dielectric properties achieved in this study?
The optimal composition (x=0.35) exhibits εr = 17.6, Q×f = 40900 GHz, and τf = −8.6 ppm/°C, indicating excellent performance for wireless communication applications.
How does the high-entropy design improve temperature stability?
The high-entropy design introduces multiple cations, which alters the [TiO6] octahedral distortion and secondary phase content, enabling tuning of τf to near-zero values.
What is the significance of the secondary phase Ca0.5Sr0.5TiO3?
The secondary phase influences the dielectric constant and quality factor; its content is inversely proportional to Q×f, and it also affects τf, allowing performance optimization.
What method was used to synthesize the ceramics?
The ceramics were synthesized using the conventional solid-phase method, which is a standard and scalable technique for producing dielectric ceramics.
What are the potential applications of these ceramics?
These ceramics are suitable for microwave resonators, filters, oscillators, phase shifters, and substrates in wireless communication systems, especially for 5G technology.
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