Hydraulic Pressure and Sintering Temperature and Time Effects on the Performance of Niobium Selenide Designed as Microwave Resonators

Herein, niobium selenide powder ceramics in pellet forms are subjected to hydraulic pressure in the range of 50–200 bar, followed by sintering at temperatures of 200 and 400 °C. The sintering at 200 °C is performed for 1 and 20 h. The properties of these powder ceramics are explored by X-ray diffraction, scanning electron microscopy (SEM), X-ray fluorescence spectroscopy, and vector network spectroscopy in the range of 9 kHz to 6.0 GHz. It is observed that NbSe2 powder pellets prefer a hexagonal/trigonal structure comprising a minor phase of monoclinic NbSe3 (∼6%). Increasing the hydraulic pressure altered the structural parameters significantly, forcing denser pellets with relative density values reaching 96.8%. Sintering the pellets at 200 °C for 1 and 20 h highly improved the relative density up to 97.7%. Longer sintering time resulted in lower strain and fewer defects as compared to those in 1 h of sintering. In addition, SEM analyses show lamellar NbSe2 platelets, with the as-pressed samples being loosely stacked with high porosity and large pores, while 1 h sintering tightens contacts and refines pores, and 20 h sintering drops the porosity further. As microwave waveguides, NbSe2 pellets are tuned by the hydraulic pressure, showing resonance at 2.64 GHz with a bandwidth of 1.55 GHz, suiting 5G/6G technology applications. The short sintering time resulted in new resonance peaks at 3.24 and 4.29 GHz. The respective bandwidths are 2.25 and 1.80 GHz. The properties of NbSe2 powder pellets are promising as smart microwave resonators for high-frequency applications, including mobile networks.