Abstract
Dense (Bi0.95Li0.05)(V0.9Mo0.1)O4-Na2Mo2O7 (100−x) wt.% (Bi0.95Li0.05)(V0.9Mo0.1)O4 (BLVMO)-x wt.% Na2Mo2O7 (NMO) composite ceramics were successfully fabricated through cold sintering at 150 °C under at 200 MPa for 30 min. X-ray diffraction, back-scattered scanning electron microscopy, and Raman spectroscopy not only corroborated the coexistence of BLVMO and NMO phases in all samples, but also the absence of parasitic phases and interdiffusion. With increasing NMO concentration, the relative pemittivity (εr) and the Temperature Coefficient of resonant Frequency (TCF) decreased, whereas the Microwave Quality Factor (Qf) increased. Near-zero TCF was measured for BLVMO-20wt.%NMO composites which exhibited εr ~ 40 and Qf ~ 4000 GHz. Finally, a dielectric Graded Radial INdex (GRIN) lens was simulated using the range of εr in the BLVMO-NMO system, which predicted a 70% aperture efficiency at 26 GHz, ideal for 5G applications.
Highlights
Microwave (MW) dielectrics are used in wireless communication systems as resonators, filters, and capacitors [1]
Phase assemblage, microstructures of ceramic pellets were characterised by X-ray powder diffraction (XRD, D2 Phaser, Bruker, Billerica, MA, USA) using CuKα radiation, scanning electron microscopy (SEM, Inspect F, FEI, Hillsboro, OR, USA) and Raman spectroscopy using a green laser with 514.5 nm at room temperature, respectively
The bulk and relative densities of Cold Sintering Process (CSP) BLVMO are 4.98 g/cm3 and 73%, respectively, which increase to 6.04 g/cm3 and 98% with the addition of NMO (Figure 1 and Table 1)
Summary
Microwave (MW) dielectrics are used in wireless communication systems as resonators, filters, and capacitors [1]. The Cold Sintering Process (CSP) has shown potential to densify ceramics/composites/. CSP was studied by Guo et al, who applied this densification method to many different microwave materials and devices, including MoO3 , LMO, Na2 Mo2 O7 , K2 Mo2 O7 , (LiBi)0.5 MoO4 and Na2 Mo2 O7 (NMO)-xPTFE composites [17,18,19,20,21,22,23,24]. Hong et al investigated the plastic deformation and densification of NaCl at room temperature [20], and Induja et al densified Al2 SiO5 ceramics using CSP with the addition of NaCl [21]. Among reported CSP microwave materials, only Na0.5 Bi0.5 MoO4 -Li2 MoO4 composites have been shown to have near zero TCF but with a comparatively low εr (17.4) [22]. The potential use CSP composites in a novel graded radial index (GRIN) dielectric lens is discussed
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