Chemical reactions of lead magnesium niobate titanate in the presence of a glass

A relaxor ferroelectric of composition 0.93Pb(Mg1/3Nb2/3)O3-0.07PbTiO3 was sintered with 3 wt.% commercial sealing glass at 750 °C for 30 min to achieve ≥95% of theoretical density and a nearly pure perovskite phase. At higher glass additions (up to 20 wt.%), higher sintering temperatures (up to 800 °C), and longer sintering times (up to 4 h), the amount of perovskite (PMN type) decreases and that of pyrochlore (6PbO · MgO · 3Nb2O5 or 3PbO · 2Nb2O5) increases. On sintering at 800 °C for 4 h no perovskite phase is present in compositions with even 1% glass addition. The reaction of glass with the PMN phase was found to lead to the disappearance of the perovskite. Addition of 0.1 to 0.6 wt.% MgO to compositions containing 1 and 3 wt.% glass (and balance PMN-PT) results in essentially pure PMN perovskite phase on sintering at 700–800 °C for 30–240 min, confirming that the reaction of glass with PMN and depletion of MgO from PMN can be arrested. The sintered ceramics exhibit relaxor behavior and possess dielectric properties essentially commensurate with the phase composition.