Structure and Microwave Dielectric Properties of Gillespite-Type ACuSi₄O₁₀ (A = Ca, Sr, Ba) Ceramics and Quantitative Prediction of the Q × f Value via Machine Learning

Abstract

Structure and dielectric properties of gillespite-type ceramics ACuSi 4 O 10 (A = Ca, Sr, Ba) were investigated by crystal structure refinement, far-infrared reflectivity spectroscopy, and microwave dielectric measurements. A series of (Ca x Sr 1−x )CuSi 4 O 10 (0 < x < 1) ceramics with relative permittivities of 5.70−5.82, Q × f values of 20391−48794 GHz (@ ∼ 13.5 GHz), and τ f of −46.3 to −38.9 ppm/°C were synthesized. By Ca 2+ substitution for Sr 2+ at the A-site, the rigid double-layered copper silicate framework remains stable, resulting in the nearly unchanged relative permittivity, while the [(Ca,Sr)O 8 ] dodecahedron undergoes shrinkage and distortion, which is correlated to the changes in the Q × f and τ f values. The normalized bond valence sums indicate that almost all ions are rattling, weakening the bond strengths and enlarging the molecular dielectric polarizability. The fitting of far-infrared reflectivity spectra reveals that the local structure changes suppress the intermediate and low-frequency vibrational modes significantly and improves the contribution from electronic polarization to permittivity. Symmetry breaking of the [(Ca,Sr)O 8 ] dodecahedron conforms to the elevated restoring forces acting on the ions and improves the τ f value. The large span in Q × f value may have intricate correlations to local structure changes and defects. Machine learning methods were introduced to explore the decisive structural factors for the Q × f value. A Q × f value prediction model correlated with the A−O2 bond length and the variance of A−O bond lengths was established. The Q × f values of isostructural (Ba y Sr 1−y )CuSi 4 O 10 ceramics were predicted and verified by experiments.

Novel Method to Achieve Temperature-Stable Microwave Dielectric Ceramics: A Case in the Fergusonite-Structured NdNbO4 System

“…Dielectric ceramics play a key role in modern microwave devices as dielectric resonators and filters, antenna substrates, class I multilayer capacitors, and low-temperature cofired ceramics (LTCCs). − With the development of 5th generation technology (5G), the demand for dielectric filters with ultrahigh-quality factors ( Q = 1/dielectric loss) is increasing for massive MIMO (multiple-input multiple-output) technology, which is widely used in the current generation of 5G base stations (sub-6 GHz). − The resonant frequency ( f ) is well-known to be proportional to the inverse square route of dielectric constant/permittivity (ε r ) ( ), and ceramics with ε r ∼ 20 (commercially referred to as K20) are suitable for dielectric filters working at sub-6 GHz with dimensions on the order of a few centimeters.…”

Advancements in Microwave Absorption Motivated by Interdisciplinary Research

“…For example, a prediction model was established based on the experimental results of (Ca x Sr 1‐x )CuSi 4 O 10 ceramics, which correlates the A–O 2 bond length and the variance of A–O bond lengths. [ 162 ] The dielectric loss ( Q × f value) of isostructural (Ba y Sr 1‐y )CuSi 4 O 10 ceramics was predicted using this model and verified through experiments (Figure 7c). Similarly, a prediction model was reported that correlates cationic radii and RL in perovskite‐RGO‐based MAMs.…”

Evolution of Phase Transformation on Microwave Dielectric Properties of BaSixO1+2x Ceramics and Their Temperature-Stable LTCC Materials

“…The Si-O bond was also strong because it is approximately 55% covalent and 45% ionic [15][16][17]. Barium silicates with high contents of SiO 4 tetrahedra and Si-O bonds demonstrated their low permittivity (ε r < 15) and high-quality factor (Q × f ), which attracted considerable attention regarding microwave dielectric materials [18][19][20][21][22]. However, 13 crystalline phases were known in the BaO-SiO 2 system [23], which indicates that the complex phase compositions might exist in barium silicates.…”