Solution route synthesis and characterization of nanocrystalline Bi2Ru2O7 for usage in resistor paste application

Abstract

In this paper, we report synthesis of Bi2Ru2O7 by solution route following the usual procedure, wherein, RuCl3 solution was added drop by drop to a solution of bismuth nitrate while maintaining the pH of reaction at 6.75 with the help of dilute HCl and NaOH. Various physico-chemico-thermal analysis of these as -precipitated powders reveal that Bi & Ru precipitate as complex hydroxides with particle size ranging between 100–200 nm. The XRD analyses of the vacuum-dried (250°C) samples indicate conversion to Bi2Ru2O7 (BRO) phase with low crystallinity having some RuO2 impurity. Further heat treatment at 600°C for 4 h in an air atmosphere produces highly crystalline Bi2Ru2O7 powder with a trace impurity of RuO2. Resistor pastes were made using these BRO powders by intimately mixing them with other ingredients such as standard lead alumino-boro-silicate glass frit and polymeric thixotropic agents like ethyl cellulose and organic solvents like butyl cellosolve and β -Terpinol. For all the paste samples, the inorganic part of the paste contained 43% glass and 57% BRO. These pastes were screen-printed and fired onto alumina substrates with pre-fired “in-house” Pd-Ag conductor terminations. The fired resistors had sheet resistance of 35–75 Ω □ and hot TCR between 150 to 480 ppm/°C and zero cold TCR for resistors No.10 & 18 and for other resistors the cold TCR deviated from zero due to low scale processing of resistor paste.