2.3.3. X-Ray Diffraction (XRD)

XRD analysis is a kind of technology that utilizes the diffraction effect of X-ray in crystal materials to analyze the structure of materials. It can be applied to the qualitative and semi-quantitative analysis of crystal phases. The X-ray diffractometer (Bruker D8 ADVANCE, Karlsruhe, Germany) was used for phase diffraction analysis. The samples were dried for 6 h in the oven at 60 °C and crushed into small pieces. Then they were ground into powders with agate mortar and sifted through a 200-mesh sieve [17]. Each group of samples was bagged with no less than 1 g of powder for diffraction analysis.