Predicting short-range order and correlated phenomena in disordered crystalline materials

Disordered crystalline materials are used in a wide variety of energy-related technologies. Recent results from neutron total scattering experiments have shown that the atomic arrangements of many disordered crystalline materials are not random nor are they represented by the long-range structure observed from diffraction experiments. Despite the importance of disordered materials and the impact of disorder on the expression of physical properties, the underlying fundamental atomic-scale rules of disordering are not currently well understood. Here, we report that heterogeneous disordering (and associated structural distortions) can be understood by the straightforward application of Pauling’s rules (1929). This insight, corroborated by first principles calculations, can be used to predict the short-range, atomic-scale changes that result from structural disordering induced by extreme conditions associated with energy-related applications, such as high temperature, high pressure, and intense radiation fields.

Quantifying amorphous and crystalline phase content with the atomic pair distribution function

Pair distribution function (PDF) analysis is a long-established technique for studying the local structure of amorphous and disordered crystalline materials. In today's increasingly complex materials landscape, the coexistence of amorphous and crystalline phases within single samples is not uncommon. Though a couple of reports have been published studying samples with amorphous and crystalline phases utilizing PDF analysis, to date little has been done to determine the sensitivity that the method currently has in resolving such contributions. This article reports a series of experiments that have been conducted on samples with known ratios of crystalline quartz and amorphous glassy silica to examine this question in detail. Systematic methods are proposed to obtain the best possible resolution in samples with unknown phase ratios and some problems that one might encounter during analysis are discussed.

Atomic pair distribution function analysis of materials containing crystalline and amorphous phases

The atomic pair distribution function (PDF) approach has been used to study the local structure of liquids, glasses and disordered crystalline materials. In this paper, we demonstrate the use of the PDF method to investigate systems containing a crystalline and an amorphous structural phase. We present two examples: Bulk metallic glass with crystalline reinforcements and Fontainebleau sandstone, where an unexpected glassy phase was discovered. In this paper we also discuss the refinement methods used in detail.