industrial systems. In most cases, the dispersed particles react Behaviors of apparent phase changes of Ru-containing more or less with the matrix phases upon firing, and many of oxides in lead borosilicate glass at high temperature have the output properties of the films are affected significantly by been investigated using X-ray diffraction and transmission the chemical stability of the dispersed phases. electron microscopy in application to thick-film resistors.Ruthenium dioxide (RuO 2 ) and lead ruthenate pyrochlore During firing of thick films containing Ru oxide powder and lead borosilicate glass frits, apparent phase changes of Ru (Pb 2 Ru 2 O 6.5 )* particles used in thick-film resistors (TFRs) are oxides have been found to occur both ways between ruthereported 1,2 to change from one phase to the other in a lead nium dioxide and lead ruthenate pyrochlore via decomposiborosilicate glass during firing at temperatures as high as tion of one phase in glass and subsequent formation of the 850ЊC. Practical thick-film paste utilizes as a glass component other. The formation of pyrochlore occurs in a lead-rich the middle proportions of the PbO-SiO 2 -B 2 O 3 system, Fig. 1, † form, Pb 2 (Ru 2؊x Pb x )O 6.5 , whereas the formation of RuO 2 is avoiding the PbO-rich, SiO 2 -rich, and B 2 O 3 -rich corners, correcharacterized by a platelike morphology instead of initial sponding respectively to compositions of high thermal expanglobular morphology. A general tendency is observed that sion rate, high melting temperature, and glass immiscibility.
RuO 2 is stable in low-PbO glass compositions and at highAccording to Bube, 1 RuO 2 , when fired in a lead borosilicate temperatures, while Pb 2 (Ru 2؊x Pb x )O 6.5 is stable in highPbO glass compositions and at low temperatures, with the implication that the stability of these phases is dictated by Table I. Chemically Analyzed Compositions of the the chemical activity of PbO in the glass melt. Binder Glasses Composition (mol%) Name PbO SiO 2 B 2 O 3