Determining the Volume Expansion at Grain Boundaries Using Extended Energy-Loss Fine Structure Analysis

Abstract

Grain boundaries (GBs) play an important role in material behavior, so considerable effort has gone into determining their structure and properties. Studies of GBs have revealed a correlation between the GB energy and expansion of the planes normal to the GB, or the so-called normal volume expansion. In this investigation, the volume expansion at several GBs was experimentally determined using extended energy-loss fine structure (EXELFS) analysis in a scanning/transmission electron microscope, allowing changes in the nearest-neighbor (n.n.) distances to be determined with nanometer spatial resolution. EXELFS performed on three-model GBs showed that the average n.n. distances at the GBs increased with increasing GB energy. Additionally, the total volume expansion at the GBs, calculated using complementary plasmon energy profiles, showed excellent agreement with volume expansions measured using other experimental techniques. Hence, this study demonstrates that EXELFS is a useful technique to measure the normal volume expansion at GBs. When combined with the results from complementary studies on the same GBs using valence electron energy-loss spectroscopy, this work further shows that the GB energy increases in relation to both the decrease in electron density at the GB and an accompanying increase in specific volume expansion at the GB.

Quantitative Characterization by Transmission Electron Microscopy and Its Application to Interfacial Phenomena in Crystalline Materials

“…A novel quantitative analysis of the physical properties using the EELS is also proposed [224][225][226][227]. The core loss edges in EELS are frequently used to analyze the physical and chemical properties related to electrons.…”

“…In contrast, Oleshko et al proposed the use of plasmon loss peaks, termed valence EELS (VEELS), to characterize the physical properties of the interphase boundary [224]. Subsequently, Nandy et al applied VEELS to grain boundaries and discussed the correlation between VEELS and the electron density and volume expansion of the grain boundary [225][226][227]. From a theoretical perspective, Kohyama et al evaluated the local energy and local stress at the surface and grain boundaries using ab initio calculations [228].…”