Nanocrystalline ZnO films of 5.8 mu m thick were sputter-deposited on ferritic carbon steel plates( 25 x 25 x 3 mm(3)) and characterized for use as ultrasonic transducers at both room temperature and high temperatures. Electrode loading effects have been studied using two types of electrodes, i.e., sputtered Cr/Au (5/50 nm) and silver paste, with electrode diameters 0.7-2.5 mm. Longitudinal and transverse waves were obtained in pulse-echo tests using both types of electrodes. With a silver paste top electrode, a dominant longitudinal mode was obtained, but with a thin Cr/Au film as the top electrode, shear waves were more dominant. Pulse-echo tests of the ZnO transducers were also performed at elevated temperatures up to 450 degrees C using a carbon paste electrodes. The sputtered ZnO films maintained a stable crystalline structure and orientation at the elevated temperatures, and ZnO devices on ferritic carbon steel could be used successfully up to 400 degrees C. However, when the temperature was increased further, rapid surface oxidation of the ferritic carbon steel caused the failure of the transducer. (C) 2014 Elsevier B.V. All rights reserved.