The effect of heating temperature in static thermal tensioning (STT) welding on mechanical properties and fatigue crack propagation rate of FCAW in steel A 36 AIP Conference Proceedings 1788, 030057 (2017) Abstract. This study reports the effect of co-doping cobalt and aluminum on the properties of ZnO-fiber piezoelectric materials. Synthesizing the ZnO-fiber piezoelectric material consisted of four steps: (1) making precursor solutions by doping aluminum and cobalt, (2) creating green fibers with an electrospinning machine, (3) sintering the fibers, and (4) testing the piezoelectricity properties. The precursor materials used were polyvinyl acetate (PVA), zinc-acetate (ZnAc), AlCl3, and CoAc. The ZnO fibers were produced in an electrospinning machine with a distance between needle tip and collector of 8 cm and a flow rate of precursor solutions at 4 μL/min. The sintering was conducted at temperatures of 400, 450, 500, 550, and 600°C for 4 hours. Piezotest was used to measure the piezoelectricity properties of ZnO or d33. The results show that the maximum value of d33 was obtained in co-doping cobalt:aluminum at a ratio of 75:25 at the sintering temperature of 500°C, which amounted to -4.1 pC/N. The ZnO-fiber-based nanogenerators co-doped with cobalt and aluminum was capable of producing energy by 218 nW/cm².