Back-scattered electron (BSE) images of polished surfaces for cold-sintered CTO-xKMO are shown in Fig. 2(a–c). Microstructures appear dense in all studied ceramic composites (also observed infracture surface of CTO-BMO, Fig. 2d), in agreement with data given in Table 1. Image contrast indicates that the microstructure is composed of two chemically discrete and distinct phases which are identified by EDS mapping (Fig. 2e-j) as KMO (light contrast) and CTO (dark contrast), respectively, consistent with XRD patterns and Raman spectra (Fig. 1). To check the compatibility of CTO-xKMO