Piezoelec. expts. on Ni-I boracite were made between 4.2 and 320 K. An automatic measuring technique permitting the detn. of the entire set of parameters of the elec. series equiv. circuit was developed and is described. It is based on the measurement of the whole admittance circle at piezoelec. resonance. The electromech. parameters d31, g31 and k231 were obtained by means of a motional capacitance method and using an independent measurement of ε33τ. Measurements were done under optical control of ferroelec. and ferromagnetic domain states. Internal loss (1/Qm) peaks were obsd. The only phase transition which can unamibiguously be confirmed is the phase transition at 61.5 K.