Indium doping effects on the structural, morphological and electrical properties of WO3 powder pellets

Tungsten oxide powders were doped with indium at weight percentages ranging from 5 to 15 wt% and pressed into pellet form under a pressure of 200 bars. The doping process was carried out using the solid-state reaction technique. The doped samples were sintered at 750 degrees C for 12 h. Both undoped and indium-doped powder pellets exhibited a triclinic structure, with hexagonal InxWO(3) emerging as a minor phase that increased with higher indium content. Indium doping increased microstrain, the percentage of stacking faults, and defect concentration while decreasing the crystallite sizes in the WO3 powder pellets. Morphological analysis of the samples revealed irregular grain shapes and sizes within the pellets. Notably, indium doping significantly reduced the porosity of WO3 from 7.42% to 3.83% as the indium content increased to 15 wt%. Electrically, the n-type resistivity increased with higher doping levels, indicating deeper donor levels. Specifically, the donor states in the powder pellets increased from 0.21 eV to 0.27 eV as the indium content rose from 5 wt% to 10 wt%, and further reached 0.29 eV at 15 wt% indium. Moreover, AC signal analysis of the powder pellets demonstrated their potential as microwave resonators suitable for antenna applications. Indium doping effectively engineered the maximum cutoff frequency, with values reaching 80 GHz in WO3 pellets doped with 15 wt% indium. These powder pellets, with thicknesses not exceeding 700 mu m and electrode areas of 3.14 x 10(-2) cm(2), show great promise for 5 G/6 G technology applications as concurrent quad-band antennas.