The thermal conductivity of ceramic materials shows a complex trend with temperature, and different types of ceramic materials exhibit different patterns. The following are some common situations:
Insulating ceramic materials
Low temperature zone (usually below Debye temperature): For insulating ceramics such as aluminum oxide (Al ₂ O3) and zirconium oxide (ZrO ₂), in the low temperature stage, as the temperature increases, the thermal conductivity shows an upward trend. This is because at low temperatures, the average free path of phonons (energy quanta of lattice vibrations) is mainly limited by internal defects, impurities, and other factors in the crystal. As the temperature increases, the number of phonons excited increases, and the interaction between phonons strengthens. Heat transfer is mainly achieved through phonons, resulting in a gradual increase in thermal conductivity. For example, the thermal conductivity of ordinary alumina ceramics will steadily increase as the temperature rises from room temperature to a certain lower temperature range.
High temperature zone (approaching or exceeding the Debye temperature): As the temperature further increases, approaching or exceeding the Debye temperature, the mean free path of phonons begins to be strongly affected by temperature. As the temperature increases, phonon scattering intensifies, and its mean free path continuously decreases, leading to a gradual decrease in thermal conductivity. Taking zirconia ceramics as an example, at higher temperatures, such as over 1000 ℃, the thermal conductivity will gradually decrease as the temperature continues to rise, and this trend will become more pronounced during the continuous heating process.
Non oxide ceramic materials
Silicon carbide (SiC) ceramics: In the lower temperature range, the thermal conductivity of SiC ceramics increases with temperature, which is also due to the increased number of phonons excited, promoting thermal conduction. However, when the temperature rises to a certain level, there will be a relatively stable plateau period in thermal conductivity, during which the effect of temperature changes on thermal conductivity becomes smaller. This is because the special crystal structure of silicon carbide itself makes its phonon scattering and other thermal conduction factors reach a relatively balanced state at this stage. As the temperature continues to rise, especially when reaching very high temperatures, the thermal conductivity will also begin to decrease due to increased phonon scattering and other reasons, but the decrease may be relatively mild compared to some oxide ceramics.
Boron nitride (BN) ceramics: At low temperatures, the thermal conductivity of BN ceramics increases with temperature, similar to the initial performance of other ceramic materials. However, during the high temperature stage, the change in thermal conductivity depends on its crystal structure type. For example, hexagonal boron nitride may gradually decrease in thermal conductivity at high temperatures, while cubic boron nitride, due to its special structure and properties, has a relatively more complex change in thermal conductivity at high temperatures. It may remain relatively stable within a certain temperature range before showing a downward trend. However, overall, it also shows a situation where thermal conductivity is affected and changes with increasing temperature.
Ceramic composite materials
For ceramic composite materials composed of multiple ceramic phases or ceramics combined with other materials, the trend of thermal conductivity variation with temperature should comprehensively consider the characteristics of each component and their interactions. For example, when a low thermal conductivity reinforcing phase is added to a ceramic matrix composite material, the overall thermal conductivity will decrease at room temperature. As the temperature increases, factors such as thermal expansion differences and interfacial interactions between the phases will affect the thermal conduction process. The change in thermal conductivity may deviate from the conventional variation law of a single ceramic material, and more complex situations such as rising first and then falling, fluctuating changes, etc. may occur, depending on the specific formula and structure of the composite material.
Overall, the thermal conductivity of ceramic materials generally shows an increasing trend with temperature (low temperature stage), and then gradually decreases under the influence of phonon scattering and other factors in the high temperature stage. However, different ceramic materials may have different specific details of changes and turning point temperatures due to their own structures, chemical bonds, and other differences.

Room termperature curing polysilazane, pls check IOTA 9150, IOTA 9150K. 
High termperature curing polysilazane, pls check IOTA 9108, IOTA 9118.