Fracture Mode and Fracture Strength of a GSO Single Crystal

Abstract

Listen

Translate article

A Ce doped gadolinium orthosilicate (Gd2SiO5:Ce, hereafter abbreviated as GSO) is one of the most promising scintillator materials [1, 2]. The fracture mode and fracture strength of the crystal provide basic information on the cracking or fracture during crystal growth processing and post-processing such as crystal handling and machining. Unlike conventional metals and ceramics, single crystals have anisotropic characteristics such as the cleavage planes and slip directions, which affect their fracture behavior. Although a few studies [3, 4] have been published on the mechanical properties of the GSO single crystal, detailed discussion has not been reported to clarify the effects of the cleavage plane and slip direction on the fracture mode and fracture strength. In the present paper, the results of threepoint bending tests of the GSO single crystal are shown to clarify them. Three-point bending test specimens were cut from a GSO bulk single crystal grown by the Czochralski method. They were 4:5 3 4:5 mm in cross-section and 50 mm in length. All the surfaces were chemically etched. A GSO is classi®ed as a monoclinic class 2=m single crystal, and the crystallographic a-axis is 17.58 inclined from the b±c plane, as shown in Fig. 1. A crystallographic Cartesian co-ordinate system X1yX 2yX 3 is taken in such a way that the X 2and X 3-axes coincide with the crystallographic b-axis ([0 1 0]) and c-axis ([0 0 1]), respectively, and the X1-axis is normal to the X2-X 3 plane or b±c plane and in the a±c plane. A GSO single crystal has the (1 0 0) cleavage plane and the [0 0 1] slip direction in the cleavage plane. Six cases of three-point bending tests were performed at a temperature of 470 K and a displacement rate of 0.2 mm miny1, as shown in Table I and Fig. 2. The cleavage plane is depicted in Fig. 2. They have the different combinations of longitudinal direction of the test specimen and loading direction. Fig. 3 shows the fracture modes observed in the three-point bending tests. In cases 1, 3, 4 and 6, the load( p)±displacement(a) curve is schematically shown in Fig. 4a, and brittle fracture occurs. Rough fracture surfaces were observed in these cases. In particular, secondary fracture in the cleavage plane