In this work, the (electro-)chemical stability of electrode interfaces of undoped, Mg-doped, and Zn-doped 0.94Na_1/2Bi_1/2TiO₃-0.06BaTiO₃ (NBT-6BT) piezoceramics were studied by in-situ X-ray Photoelectron Spectroscopy (XPS) measurements. Electrochemical cells were fabricated using the low work function material tin-doped indium oxide (ITO: 2 nm) as the top cathode and platinum as the bottom anode. Two kinds of high-temperature in-situ XPS measurements with and without bias were performed to investigate the interface between NBT-6BT and ITO. Heating in XPS can release part of oxygen from ITO into vacuum, which shifts the Fermi level in the ITO upward, and the Fermi level of NBT-6BT also moves up with ITO. At high temperature XPS measurement without bias, the binding energy of Bi³⁺ 4f_7/2 increases to 159.5 eV. However, this increase is not enough to induce an interface reduction. In order to further shift the Fermi level of ITO up, the ITO was used as a cathode such that oxygen vacancies were expected to move from NBT-6BT to ITO through the interface. In these experiments, metallic Bi starts to develop when the binding energy of the Bi 4f_7/2 reaches about 159.7 eV. This level corresponds to the reduction potential, namely the upper limit of the Fermi level of NBT-6BT. The appearance of metallic Bi (electrochemical reduction) indicates that the cathodic interface is unstable. Such experiments can help to understand the instability of electrode interface and improve the performance of NBT-based multilayer actuators, transducers, and ceramic capacitors.