High-entropy engineering has emerged as an effective strategy for tailoring structural disorder and functional responses in tetragonal tungsten bronze (TTB) ferroelectrics. However, how configurational entropy, crystal structure, modulation characteristics, and relaxor dynamics govern the macroscopic electrical response remains insufficiently understood. Here, K(NaPr)_1-x(SrBa)_xNb₅O₁₅ ceramics with continuously varying configurational entropy were designed to investigate the origin of relaxor-ferroelectric evolution. With increasing Sr/Ba substitution, the electrical response evolves from an ergodic-relaxor state with slim hysteresis loops and four current peaks to a ferroelectric-like state with double current peaks, fatter loops, and increased remanent and maximum polarizations. This evolution is accompanied by increased lattice parameter c and tetragonality (c/a), indicating a structural evolution toward a more stable polar state. The dielectric anomalies and Vogel-Fulcher analysis further reveal an increase in freezing temperature and a decrease in activation energy, indicating strengthened coupling among polar nanoregions and a gradual evolution from the relaxor state toward a non-ergodic relaxor or ferroelectric state. Notably, this trend is opposite to the commonly expected enhancement of relaxor behavior in high-entropy systems, suggesting that configurational entropy does not simply strengthen relaxor characteristics through increased compositional disorder. Instead, configurational entropy modulates the order-disorder state of A-site occupation, thereby changing the octahedral tilting patterns and the modulation structure, which affects the diffuseness of the phase transition. These results demonstrate that the macroscopic electrical response in the high-entropy K(NaPr)_1-x(SrBa)_xNb₅O₁₅ system is regulated by crystal structure, modulation structure, and polar nanoregion dynamics, providing new insight into the relaxor behavior of TTB ferroelectrics.

Microwave dielectric ceramics (MWDCs) are pivotal to modern wireless communication systems, with their performance governed by three key parameters: relative dielectric constant (ε_r), Q×f value (product of quality factor Q (reciprocal dielectric loss) and frequency f), and temperature coefficient of resonant frequency (τ_f). This review systematically summarizes the recent research progress on MWDCs from five interrelated aspects. In terms of performance characterization, standardized resonant methods achieve ε_r measurement errors below 1% and a dielectric loss (tanδ) detection limit as low as 10⁻⁵. Theoretically, frameworks from complex crystal chemistry to the recently elucidated cation rattling effect enable quantitative interpretation of dielectric behavior. In processing, the cold sintering process achieves ceramic densification below 300 °C, reducing energy consumption by over 97% in comparison with conventional sintering. For applications, these materials have been widely deployed in high-performance substrates, resonators, and filters for 5G/6G communications, with device insertion loss maintained below 1 dB. Additionally, data-driven approaches, particularly machine learning, can accurately predict key dielectric properties with a coefficient of determination (R²) higher than 0.9, accelerating the exploration and development of novel MWDCs. By integrating these perspectives, this review offers systematic insight into the state-of-the-art progress and future development directions of MWDC research.

The rapid development of fifth-/sixth-generation telecommunication technologies has increased the demand for silicate ceramic materials with low permittivity and low dielectric loss. However, few silicate ceramics with ultrahigh Q×f values (≥ 200,000 GHz) have been developed to date. In this study, a slight substitution of Ge⁴⁺ ions in MgSi_1−xGe_xO₃ (MSGx, x = 0 to 0.6) ceramics caused a phase transition from clinoenstatite (x = 0) to orthoenstatite (x = 0.2), and the Q×f value increased from 70,600 GHz to 148,800 GHz. Following the phase transition, the cations change from a “compressed” state to a “rattle” state, and the lattice distortion continues to rise with x, resulting in the optimal microwave dielectric properties (ε_r = 7.21, Q×f  = 259,300 GHz) of the MgSi_0.5Ge_0.5O₃ ceramics. Significant discrepancies in the dielectric properties are found in the microwave and terahertz bands. There is an anomalous increase in ε_r and a decrease in the Q×f value in the terahertz band, which is due to the change in polar phonon modes revealed by the terahertz time-domain spectra. Consequently, MgSi_0.7Ge_0.3O₃ ceramics display superior dielectric properties, with ε_r = 7.02, Q×f  = 191,300 GHz in the terahertz band. These novel materials have the potential to serve as promising dielectric materials for future microwave or terahertz mobile communication systems.