The crystal structure and dielectric properties of $(Pb_{1-x}Ba_x)(Mg_{1/2}W_{1/2})O_3$ systems have been investigated by x-ray diffraction and dielectric constant measurements. From the results of the dielectric measurement it is shown that both the transition temperature ($T_c$) and the maximum dielectric constant decrease with increasing Ba substitution contents(x). The maximum dielectric constant and the transition temperature are independent of the measuring frequencies.
The crystal structure change in conjunction with the lattice parameter variation and modulation wave vector also has been investigated from -200 to 50℃ by using x-ray diffraction of the calcined power. The low temperature x-ray results show that $Pb_{1-x}Ba_xMg_{1/2}W_{1/2}O_3$ solid solution system has two modulation wave vectors, $q_1$=(110) and $q_2$ = (1/2 1/2 0), in the low temperature phase. These modulation wave vectors disappear at different temperatures at the paraelectric-antiferroelectric transition. The temperature difference at which two modulation wave vectors disappear does not vary noticably with the Ba concentration. It is also shown that the intensity of modulation lines decreases with increasing contents of Ba substitution. This may be interpreted that the antiferroelectric displacement of Pb ions decreases. In general, it is well known that the antiferroelectric materials undergo the negative volume change in the paraelectric-antiferroelectric(PE-AFE) transition. However, we observed that the unit cell volumes both of $Pb_2MgWO_6$ and its Ba-substituted solid solutions increases at the PE-AFE transition. This anomalous behavior of the $Pb_2MgWO_6$-based solid solution is also discussed in conjunction to the antiferroelectric displacement of Pb ions and the volume change of the unit cell due to the Ba concentration variation.
