The Crystal Structure and phase transition behavior in $(Pb_{1-x}Sr_x)(Mg_{1/2}W_{1/2})O_3$ system have been investigated by dielectric measurement, P-E hysteresis loop measurement, X-ray and transmission electron diffraction experiments. Two phase transitions are found from dielectric measurement. The first transition point in the high temperature side almost does not change but the second transition temperature moves to the lower temperature fast with increasing of Sr-content. The intermediate phase shows linear behavior of antiferroelectric character in the P-E hysteresis loop measurement and the low temperature phase does too.
The crystal structure change has been studied in conjunction with the two modulations $q_1$ = (1/2 1/2 0) and $q_2$ = (1/4 1/4 0) and lattice parameters have been calculated from liquid nitrogen temperature to room temperature on the base of X-ray diffraction patterns. The specimen of x = 0.08 has been especially observed by transmission electron microscopy to confirm and complement the result of X-ray diffraction at various temperatures. The continuous phase transition occurs in the system. That is, only $q_1$ = (1/2 1/2 0) modulation appears in the intermediate phase and both $q_1$ = (1/2 1//2 0) and $q_2$ = (1/4 1/4 0) modulation exist in the low temperature phase. TEM observation showed the spots with $q_1$ = (1/2 1/2 0) that could not be detected in XRD. It means that the possibility of in-phase tilting or the local cation antiparallel shift over the transition temperature. In contrast with the positive volume change of $Pb_2MgWO_6$ in the paraelectric - antiferroelectric transition the Sr-substituted system shows volume reduction. Especially the c-axis undergoes gradual contraction all the way in the intermediate region while the a-axis is nearly constant in the temperature dependence of lattice parameters. It seems that $q_1$ = (1/2 1/2 0) modulation is accompanied by less distortion than the sum of $q_1$ = (1/2 1/2 0) and $q_2$ = (1/4 1/4 0) modulation does.
