Low-permittivity and low dielectric loss in co-fired Na2O–Bi2O3–Ln2O3–MoO3 (Ln = Sm0.3Y0.7) microwave dielectric ceramics

This study examines the microwave dielectric properties of the Na 2 O–Bi 2 O 3 –Ln 2 O 3 –MoO 3 (Ln = Sm and Y) system, synthesized via a solid-state process at ultra-low sintering temperatures ranging from 600°C to 660°C. The X-ray diffraction and Rietveld refinement results suggested that a tetragonal sheelite phase was found in the x Na 5 Bi(MoO 4 ) 4 –(1− x )Na 5 Ln(MoO 4 ) 4 (0.05 ≤ x ≤ 0.20) ceramics. Scanning electron microscopy (SEM), backscattered electron image (BSE) and energy dispersive spectrometer (EDS) results indicated that the complex substitution of Bi 3+ produced a significant effect on the microstructural morphology. Besides, the substitution of Bi 3+ for (Sm 0.3 Y 0.7 ) 3+ effectively reduced the sintering temperature to 630°C. The variation of theoretical dielectric polarizabilities (α theo. ), the polarizability density (α theo. / V m ), the observed dielectric constant (ε r ), theoretical dielectric constant (ε theo. ), packing fraction (PF) values, and bond valence ( V i ) as a function of x value were investigated, which was helpful for understanding microwave dielectric properties. The ceramic composition 0.1Na 5 Bi(MoO 4 ) 4 –0.9Na 5 Ln(MoO 4 ) 4 sintered at 630°C for 2 h demonstrated the best microwave dielectric properties, exhibiting a ε r ∼ 9.3, Q × f value of about 31,200 GHz (at 11 GHz) and a temperature coefficient (τ f ) of −41.3 ppm/°C. Both XRD and EDS results indicated that the 0.1Na 5 Bi(MoO 4 ) 4 –0.9Na 5 Ln(MoO 4 ) 4 ceramic was chemically compatible with Ag at its sintering temperature (630°C). The x Na 5 Bi(MoO 4 ) 4 –(1− x )Na 5 Sm 0.3 Y 0.7 (MoO 4 ) 4 (0.05 ≤ x ≤ 0.20) ceramics in the Na 2 O–Bi 2 O 3 –Ln 2 O 3 –MoO 3 (Ln = Sm and Y) system are promising candidates for 5G and its successor 6G mobile communication technology.