Characterizing the Structure of Highly-Alloyed Electroceramics

Ceramics, as a class of material, are of foundational importance to modern electronics. From silicon to the titanates, open up any modern electronic device and you will find that its operation is wholly reliant on ceramic materials and their unique properties. One way in which these electroceramics are engineered to access specific, desirable properties is by modifying their composition. In this work, we study several highly alloyed ceramic materials, which we define as materials which have a large amount (tens of mole percent) of a single substituent element, making this class of materials distinct from both doped materials, which incorporate only small amounts of a substituent element, and from true high-entropy alloys, which typically incorporate at lease five different elements. We examined three of these highly alloyed electroceramics: Ba(Ti_0.6Zr_0.4)O₃ (BZT), (Al_0.7Sc_0.3)N ((Al,Sc)N), and (Al_1-xGd_x)N ((Al,Gd)N). In BZT we sought a spatial correlation between regions locally enriched in Ti and polar nanoregions. We were unable to detect any regions which were statistically significantly enriched in Ti, although polar nanoregions were detectable. In (Al,Sc)N an attempt was made to reduce leakage current by growing the film atop a lattice-matched substrate, however the leakage current was instead found to be worsened. We found this to be due to an increase in the roughness of the film-substrate interface, leading to an increase an the effective electric field at the interface and corresponding increase in leakage. In (Al,Gd)N we analyzed a compositionally-graded thin film sample to assess the non-equilibrium structure of the sputtered film as a function of composition. We found that increasing levels of Gd incorporation led to a loss of long-range structural order, while electron energy loss spectroscopy revealed that the local structure remained wurtzite-like for all studied compositions.