Structural and Photoacoustic Study of Cr11Ge19 Prepared by Mechanical Alloying

Abstract

A nanostructured Cr11Ge19 phase was produced by mechanical alloying for 15 h. Decomposition occurred for larger milling times, yielding Cr, Ge, Cr2O3 and GeO2. According to the Cr-Ge phase diagram, the Cr11Ge19 phase is stable up to ≈ 928 oC, but, when submitted to milling, a structural instability causes its decomposition. We studied this structural instability using the coordination numbers and interatomic distances of bulk Cr11Ge19 to simulate the structure factors SCrCr(K), SCrGe(K), and SGeGe(K). The radial distribution functions RDFCrCr(R), RDFCrGe(R) and RDFGeGe(R) were obtained by Fourier transforming the Sij(K) factors, and an important chemical disorder up to ≈7 Å was observed in the RDFCrGe(R) and RDFGeGe(R) functions. This chemical disorder was quantified using Cowley-Warren α ij CW parameter. The thermoelectric properties of the Cr11Ge19 phase were also studied.

Keywords

• Mechanical alloying
• X-ray diffraction
• Rietveld method
• Photoacoustic absorption spectroscopy
• Thermal diffusivity