STRENGTH AND TOUGHNESS OF BARIUM-TITANATE CERAMICS

The effect of processing variables on the mechanical and electrical properties of holmium-doped barium titanate ceramics with a positive temperature coefficient of resistance has been investigated. This paper contains details of the tests used to measure the mechanical properties of ceramics prepared using four compositional mixes. Two methods of measuring strength were used: diametral compression of disc samples and four-point bending of beam specimens. Fracture toughness was also evaluated using two methods: the failure of single edge-notched (SEN) beams under four-point loading and cracking from a surface indentation with a diamond pyramid indentor. Values of strength ranged from 18 to 82 MPa for the four materials when measured by the diametral compression test. This compared with a range of 35-79 MPa for the same materials tested in pure bending. Fracture toughness values ranged from 0.65 to 0.95 MPa ml 12 for the SEN specimens and from 1 to 1.8 MPa m1/2 using the indentation technique on the same samples.