Effect of Glass Composition on the Thermal Expansion of Relict Crystals of RuO<sub>2</sub> in Doped Lead-Silicate Glasses (Thick Film Resistors)
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Abstract
The thermal expansion coefficients (TEC) of RuO<sub>2</sub> crystallits in thick film resistor (TFR) composites, consisting of RuO<sub>2</sub> dispersed in lead-silicate glass of various compositions, were evaluated from X-ray diffraction patterns at temperatures 298; 773; 973 and 1123 K corresponding to characteristic temperatures of resistivity and thermopower anomalies of the TFRs. It has been found that TEC of free RuO<sub>2</sub> powder along a-axis has an anomaly at T > 973 K (expansion is replaced by constriction), whereas constriction along c-axes remains for all temperatures. This anomaly disappears in doped glass of simplest composition (2SiO<sub>2</sub>.PbO) but occurs in glasses of some complex compositions. Symmetry of unit cell of RuO<sub>2</sub> is not changed in the temperature range investigated.
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