Perovskite nitrides: A new playground for functional materials

The perovskite crystal is a favorite playground for electroceramists across a wide variety of applications, and recent developments on hybrid metallorganic perovskite photovoltaics has renewed interest in expanding the chemical space of this flexible and multifunctional crystal structure. A survey of experimentally confirmed simple perovskite compounds (ABX3) finds no reports of pure X=N anion chemistries. One challenge of forming nitride perovskite materials is the high valence cations needed to satisfy the high valency of nitrogen; another is limiting oxygen impurities. Computational predictions of energetically favorable nitride perovskites have been reported[1] and DFT+LDA methods[2] suggest that the lowest energy state of LaWN3 is a non-centrosymmetric R3c type distorted perovskite structure with a spontaneous polarization of approximately 60µC/cm2 along the \u3c111\u3e polar axis. A relatively low energy barrier predicted for polarization reversal raises the possibility of ferroelectricity as well. Developing a ferroelectric nitride would greatly simplify integration of a number of functional (e.g., ferroelectric, piezoelectric, and more) properties directly with nitride semiconductors for a variety of integrated sensing and energy conversion applications. Here we report the experimental confirmation of oxygen-free LaWN3 as a perovskite (Fig. 1) using multiple fabrication approaches. Calculations show 5 different symmetries with very similar lattice energies (3 polar and 2 non-polar); refinements of x-ray and electron diffraction in conjunction with property measurements document the complexity of the LaWN3 system in addition to other closely-related perovskite nitrides. [1] R. Sarmiento-Pérez et. al., Chemistry of Materials, 27, 5957 (2015) [2] Y. Fang et. al., Physical Review B,95, 014111 (2017) Please click Additional Files below to see the full abstract

Replace Yourself: Some Student Advisors\u27 Perspectives on Ceramic Education

The ACerS President\u27s Council of Student Advisors (PCSA) is a group of undergraduate and graduate ceramics students. The ACerS Young Professionals Network provides opportunities for early-career ceramists to become actively involved in the Society and to develop the network of peers that enhance the personal and professional aspects of their ceramics careers. The PCSA is mentored by volunteers representing the ACerS board of directors, education integration committee NICE, ceramic education council, Keramos, and the materialaAdvantage committee. The PCSA relies is supported by ACerS, its divisions and sections, corporate members, and donations from some individual members to finance its annual business meeting, held in conjunction with the ACerS board of directors meeting in January every year

High-Speed and High-Power Ferroelectric Switching Current Measurement Instrument for Materials with Large Coercive Voltage and Remanent Polarization

A high-speed and high-power current measurement instrument is described for measuring rapid switching of ferroelectric samples with large spontaneous polarization and coercive field. Instrument capabilities (±200 V, 200 mA, and 200 ns order response) are validated with a LiTaO3 single crystal whose switching kinetics are well known. The new instrument described here enables measurements that are not possible using existing commercial measurement systems, including the observation of ferroelectric switching in large coercive field and large spontaneous polarization Al0.7Sc0.3N thin films

Switching it Up: New Mechanisms Revealed in Wurtzite-type Ferroelectrics

Wurtzite-type ferroelectrics have drawn increasing attention due to the promise of better performance and integration than traditional oxide ferroelectrics with semiconductors such as Si, SiC, and III-V compounds. However, wurtzite-type ferroelectrics generally require enormous electric fields, approaching breakdown, to reverse their polarization. The underlying switching mechanism(s), especially for multinary compounds and alloys, remains elusive. Here, we examine the switching behaviors in (Al,Sc)N alloys and new wurtzite-type multinary candidate compounds we recently computationally identified. We find that switching in these tetrahedrally-coordinated materials proceeds via a variety of non-polar intermediate structures and that switching barriers are dominated by the more electronegative of the cations. For (Al,Sc)N alloys, we find that the switching pathway changes from a collective mechanism to a lower-barrier mechanism enabled by inversion of individual tetrahedra with increased Sc composition. Our findings provide insights for future engineering and realization of wurtzite-type materials and open a door to understanding domain motion