An in-house built stiff bending device (Institute of Advanced Ceramics, Hamburg University of Technology) was used for 3-point-bending tests of bulk samples cut with a diamond saw into bars of spatial dimensions, h × w × l, of ∼ 1.2 × 1.2 × 10 mm. The span of lower support was l s = 7.1 mm. The applied loading speed was 2 µm s -1 and displacements were recorded using an inductive position encoder. Elastic moduli were calculated from the linear parts of the force-displacement-curves. The stress was calculated acc. to σ = 3F l s /(2wh 2 ).