Due to their superior piezoelectric coefficients, PZN-PT ($(1- x)$Pb(Zn$_1/3$Nb$_2/3$)O$_3- x$PbTiO$_3$) and PMN-PT [$(1- x)$Pb(Mg$_1/3$Nb$_2/3$)O$_3- x$PbTiO$_3$] are viewed as possible substitutes for conventional PZT in advanced piezodevices. This paper presents noncontact displacement measurements in small rectangular PZN-PT and PMN-PT crystal rods. We propose a new phase-shift-interferometry-based technique for static and dynamic axial displacement measurement. The measurement technique makes use of the fact that the sinusoidal intensity data from the same pixels in two interferograms with different phase shifts form an elliptic Lissajous curve. We can accurately estimate phase-shift steps by fitting the elliptic Lissajous curve by least squares. Actuator displacements are then calculated from the estimated phase-shift steps. In this paper, the proposed technique was integrated with a Mirau interferometeric microscope with a machine vision system. This optomechatronic measurement system was used to measure the piezoelectric coefficient$d_31$of$langle 001rangle$-poled PZN-PT and PMN-PT single crystals as well as hysteresis. Simulations and experiments demonstrate that the proposed technique is robust against the influence of intensity noise in interferograms.