The carbonization of various types of metal–organic frameworks (MOFs) was carried out under N2 gas flow and high temperature. The formation of carbonized MOFs (CMOFs) was monitored by Raman spectroscopy. In addition to the well-known D and G bands in Raman spectra, the salient G′ band feature was observed only in Mn-, Fe-, Co-, and Ni-containing CMOFs. On the other hand, CMOFs containing other metals (Al, Cr, V, Cu, and Zr) do not show the G′ band. Furthermore, the G′ band was also observed when we mixed the nitrate salts of Mn­(II), Fe­(III), and Co­(II) with Al-containing MOFs using the same treatment conditions as in the formation of CMOFs. The G′ band is known to be related to the stacking order of graphitic layers. The presence of the Raman G′ band in CMOFs can be ascribed to the catalytic activity of Mn, Fe, Co, and Ni. The trend of the G′ band to G band intensity ratio resembles the “volcano curve” in the description of the behavior of catalytic activities of transition metals. The G′ bands in Mn-, Fe-, Co-, and Ni-containing CMOFs were well-fitted with two-component peaks which indicates that these CMOFs have well-stacked graphitic structures.

Y2O3 is a common sintering additive of AlN ceramics to achieve densification and remove the oxygen impurity, resulting in a typically grain boundary phase (GBP) Y3Al5O12 (YAG). Two AlN ceramics with 3wt% and 5wt% Y2O3 intended for thermal conductivity study were sintered at 1800 °C for 4h. X-ray diffraction (XRD) indicates that GBP could either be YAG or YAP (YAlO3) phase, while the selected area electron diffraction (SAED) and energy dispersive X-ray (EDX) in TEM identifies it as YAP instead of YAG. The electron back-scattering diffraction (EBSD) in SEM further confirms the general presence of YAP phase in both samples. In meanwhile, two types of Al-rich GBPs were also detected by TEM, which could account for extra dopant in the microstructure. GBP contents in the both samples were quantified by K-value method (XRD) and from backscattered electron images. Such analyses of GBPs are helpful to understand the sintering mechanism and evaluate their contribution to the thermal conductivity of AlN.

Metal–organic frameworks (MOFs) containing V, Cr, Mn, Fe, Co, Ni, Cu, and Zr were pyrolyzed under nitrogen flow. The products of carbonized MOFs (CMOFs) contain metal oxides and carbonaceous residues, which were characterized by powder X‐ray diffraction (PXRD), electrical conductivity (EC), and Raman spectroscopy. To remove the metallic components in CMOFs, hydrofluoric acid (HF) treatment was performed. PXRD analysis showed that only Mn, Co, Ni, and Zr, but not V, Cr, Fe, and Cu, could be completely removed from CMOFs after HF treatment. In fact, PXRD analysis also revealed that during the formation of CMOFs, not only metal oxides, but also metal carbides were formed. The change of the EC of CMOFs after HF treatment was found to be mainly contributed from the metal components, whereas the carbon (graphitic) components played minor roles. The effect of HF treatment on the structure of CMOF was not significant as verified by the Raman analysis of the intensity ratio between D band and G band.