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The demand to discover new materials is scientifically as well as industrially a continuously present topic, covering all different fields of application. The recent scientific work on thin film materials has shown, that especially for nitride-based protective coatings, computationally-driven understanding and modelling serves as a reliable trend-giver and can be used for target-oriented experiments. In this study, semi-automated density functional theory (DFT) calculations were used, to sweep across transition metal diborides in order to characterize their structure, phase stability and mechanical properties. We show that early transition metal diborides (TiB2, VB2, etc.) tend to be chemically more stable in the AlB2 structure type, whereas late transition metal diborides (WB2, ReB2, etc.) are preferably stabilized in the W2B5−x structure type. Closely related, we could prove that point defects such as vacancies significantly influence the phase stability and even can reverse the preference for the AlB2 or W2B5−x structure. Furthermore, investigations on the brittle-ductile behavior of the various diborides reveal, that the metastable structures are more ductile than their stable counterparts (WB2, TcB2, etc.). To design thin film materials, e.g. ternary or layered systems, this study is important for application oriented coating development to focus experimental studies on the most perspective systems.

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While many research activities concentrate on mechanical properties and thermal stabilities of protective thin films, only little is known about their thermal properties being essential for the thermal management in various industrial applications. Based on the 3x-method, we show the influence of Al and Cr on the temperature dependent thermal conductivity of single-phase cubic structured TiN and single-phase wurtzite structured AlN thin films, respectively, and compare them with the results obtained for CrN thin films. The dc sputtered AlN thin films revealed a highly c-axis oriented growth for deposition temperatures of 250 to 700 C. Their thermal conductivity was found to increase strongly with the film thickness, indicating progressing crystallization of the interface near amorphous regions during the sputtering process. For the 940 nm AlN film, we found a lower boundary for the thermal conductivity of 55:3 W m À1 K À1. By the substitution of only 10 at. % Al with Cr, j significantly reduces to $5:0 W m À1 K À1 , although the single-phase wurtzite structure is maintained. The single-phase face centered cubic TiN and Ti 0.36 Al 0.64 N thin films exhibit j values of 3:1 W m À1 K À1 and 2:5 W m À1 K À1 , respectively, at room temperature. Hence, also here, the substitutional alloying reduces the thermal conductivity, although at a significantly lower level. Singlephase face centered cubic CrN thin films show j values of 3:6 W m À1 K À1. For all nitride based thin films investigated, the thermal conductivity slightly increases with increasing temperature between 200 and 330 K. This rather unusual behavior is based on the high defect density (especially point defects) within the thin films prepared by physical vapor deposition. Published by AIP Publishing.