Decomposition of Ruthenium Oxides in Lead Borosilicate Glass

Behaviors of apparent phase changes of Ru-containing oxides in lead borosilicate glass at high temperature have been investigated using X-ray diffraction and transmission electron microscopy in application to thick-film resistors. During firing of thick films containing Ru oxide powder and lead borosilicate glass frits, apparent phase changes of Ru oxides have been found to occur both ways between ruthenium dioxide and lead ruthenate pyrochlore via decomposition of one phase in glass and subsequent formation of the other. The formation of pyrochlore occurs in a lead-rich form, Pb₂(Ru_{2? x} Pb _x )O_6.5, whereas the formation of RuO₂ is characterized by a platelike morphology instead of initial globular morphology. A general tendency is observed that RuO₂ is stable in low-PbO glass compositions and at high temperatures, while Pb₂(Ru_{2? x} Pb _x )O_6.5 is stable in high-PbO glass compositions and at low temperatures, with the implication that the stability of these phases is dictated by the chemical activity of PbO in the glass melt.