Temperature stable Sm(Nb1−xVx)O4 (0.0 ≤ x ≤ 0.9) microwave dielectric ceramics with ultra-low dielectric loss for dielectric resonator antenna applications

Abstract

Herein, the structure and dielectric properties of Sm(Nb_1−xV_x)O₄ (SNV-x) (0.0 ≤ x ≤ 0.9) ceramics were studied by crystal structure refinement, Raman, transmission electron microscope (TEM), far-infrared/THz reflectivity spectroscopy and microwave dielectric tests. Three kinds of ultra-low dielectric loss and temperature-stable Sm(Nb_1−xV_x)O₄ (0.2 ≤ x ≤ 0.4) ceramics with permittivities of 18.01–16.89, Q × f values of 97 800–75 200 GHz (@∼8.6 GHz), and TCF of −5.6 (x = 0.2), to +2.3 ppm °C⁻¹ (x = 0.3), then −6.3 (x = 0.4) ppm °C⁻¹ were synthesized in this system. It was found that V⁵⁺ substitution can reliably induce the phase transition of monoclinic fergusonite (M-fergusonite, I2/a) to tetragonal zircon phase (T-zircon, I4₁/amd) (x ≈ 0.3), while effectively reducing the phase transition temperature. TEM shows that there were two different orientation domain structures in the M-fergusonite phase, and the widths of the two domain structures get closer with an increase in B-site substitution. Moreover, the variations in permittivity (ε_r), quality factor (Q × f), and the temperature coefficient of resonance frequency (TCF) were strongly related to the crystal distortion and phase transition. Notably, a rectangular dielectric resonator antenna (RDRA) was fabricated with an Sm(Nb_0.8V_0.2)O₄ (SNV-0.2) specimen. The antenna resonated at 27.04 GHz and had a bandwidth of ∼820 MHz (S11 < −10 dB). This system is a good candidate for 5G and future millimeter-wave applications.