On the Origin of Chemically Graded Metal/Ceramic Interface

Abstract

A gradual variation in chemical composition at an atomic level in a metal/ceramic interface would result in a gradual variation in structural features that can give rise to unusual properties of the heterostructure. One of the ways such atomic-level chemical gradation can be achieved is by diffusion of anions from ceramic to metal. This process is perceived to be unfavorable because it requires the creation of anion vacancies in ceramic and anion interstitials in metal. We use the sum of C, N, or O vacancy formation energy in ceramics and their interstitial formation energy in metals to assess the possibility of migration of anions across the metal/ceramic interface, leading to an atomically chemically graded interface. We use the first-principles density functional theory to calculate the driving force for a few scientifically and technologically important metal/ceramic systems: a combination of 10 metals (M=Ti, Zr, Hf, V, Nb, Ta, Mg, Al, Cr, and Fe) and corresponding 30 ceramics MaXb (X=C, N, and O). The metal/ceramic systems that favor chemical gradation have metals from group IVB and VB mainly due to the large negative interstitial formation energies.