Performance of ITO, NiCr, and Pd thick film electrodes on lithium niobate under high-temperature operation  

Reliable electrical contacts are essential for high-temperature piezoelectric devices based on lithium niobate (LiNbO₃, LN), yet the behavior of electrode materials under elevated temperatures remains insufficiently studied. Here we evaluate three practical electrode systems on bidomain LN (BLN) substrates: screen-printed Pd thick films, sputtered indium–tin oxide (ITO), and sputtered nichrome (80 wt.% Ni and 20 wt.% Cr). Bidomain LN crystals function as single-crystal piezoelectric bimorphs with well-defined bending resonances, enabling sensitive impedance-based detection of electrode degradation. Impedance spectra were recorded in 100 °C increments up to 800 °C, complemented by microstructural inspection, electrical resistivity measurements, and X-ray photoelectron spectroscopy. Pd thick films showed the highest stability, with unchanged impedance spectra after heating to 800 °C and cooling. Indium–tin oxide electrodes remained functional up to at least 700 °C, with possible operation at 800 °C. X-ray photoelectron spectroscopy results suggest gradual incorporation of Nb from the BLN substrate which may initiate slow degradation in ITO. NiCr electrodes showed degradation of electrical contact near 500 °C due to oxide formation, while intrinsic electrical degradation associated with loss of film continuity occurred above 600 °C. These results identify Pd as a robust but costly choice, ITO as a promising mid-range alternative, and NiCr as suitable only within a lower high-temperature window.