Structure and low-temperature thermal conductivity of pyrolytic boron nitride

The microstructure and morphology of three samples of pyrolytic boron nitride deposited at different temperatures have been characterized with use of x-ray diffraction and thermal-conductivity measurements. The x-ray analysis allowed the determination of the mean interlayer spacing, the out-of-plane coherence length, and the crystallites preferred orientation. It revealed the presence of three distinct morphologies. The thermal conductivity was measured as a function of temperature in the range 1. 5 < T < 300 K. The temperature variations of the thermal conductivity were fitted by using a model previously developed for the analysis of the thermal conductivity of graphites and carbons. This fit allowed the determination of the in-plane coherence length. It also allowed the analysis of point-defect concentration and of the interlayer shear modulus. It is shown that low-temperature thermal-conductivity measurements may be used to complement x-ray diffraction data for the microstructural characterization of materials.