Ultra-low temperature co-fired ceramics with adjustable microwave dielectric properties in the Na2O–Bi2O3–MoO3 ternary system: a comprehensive study

Abstract

Herein, a series of microwave dielectric materials in the Na₂O–Bi₂O₃–MoO₃ ternary system, such as Na₂MoO₄, Na₆Mo₁₀O₃₃, Na₂Mo₂O₇, Bi₂Mo₃O₁₂, Bi₂Mo₂O₉, and Bi2MoO6, were studied via phase identification, microstructure characterization, spectral analysis and microwave dielectric property tests; all the samples of each component could be sintered below 750 °C. Three different kinds of bulk ceramics, x(NaBi)_0.5MoO₄–(1−x)Na₂MoO₄ (x = 0.2–0.6), x(NaBi)_0.5MoO₄–(1−x)Bi₂MoO₆ (x = 0.6, 0.8) and 0.5(NaBi)_0.5MoO₄–0.5Bi₂Mo₂O₉, were considered as the main research objects in this work. The sintering temperature of the x(NaBi)_0.5MoO₄–(1−x)Na₂MoO₄ (x = 0.2–0.6) composite ceramics ranged from 600 °C to 640 °C; high-performance microwave dielectric properties with relative permittivities in the range of 8.9–16.2, Q_f (quality factor) values in the range of 11 050 GHz–8,900 GHz, and τ_f values ranging from −27–11 ppm °C⁻¹ could be obtained in these ceramics. For the x(NaBi)_0.5MoO₄–(1−x)Bi₂MoO₆ (x = 0.6, 0.8) composite ceramics, a near-zero τ_f value (−2.6 ppm °C⁻¹) was achieved with the 0.8(NaBi)_0.5MoO₄–0.₂Bi₂MoO₆ ceramic sintered at 720 °C with a middle-permittivity of 32.6 and a Q_f value of 14570 GHz. The multiphase ceramic 0.5(NaBi)_0.5MoO₄–0.5Bi₂Mo₂O₉ could be sintered at 680 °C; the dense sample had a relative permittivity of 35.7, a Q_f value of 9780 GHz and a small positive τ_f value of 17 ppm °C⁻¹. As this study shows, the Na₂O–Bi₂O₃–MoO₃ ternary system had a lot of new composite ceramics with low sintering temperatures and great microwave dielectric properties. All these materials could be regarded as candidates applicable to LTCC/ULTCC technology.