Diffuse scattering from an Al₇₂Ni₂₀Co₈decagonal quasicrystal on an order disorder transformation

Abstract

Non-uniform distortion induced by superstructure domains has been observed during the ordering process of an order-disorder transformation in a single decagonal quasicrystal of Al 72 Ni 20 Co 8 . The full width at half maximum (FWHM) of the fundamental reflections increased below the transformation temperature, T c . At the same time, the integrated intensity of the fundamental reflections varied drastically at T c . A small hysteresis was also observed in the temperature dependences of both the FWHM and the integrated intensity of the fundamental reflections. Peak broadening of the fundamental reflections is predominantly dependent on |G | below T c . In addition, the weak dependence of the peak broadening with |G ⊥ | is extracted from the observed FWHM of the fundamental reflections. After deconvolution, the FWHM of the fundamental reflections appears to be a linear combination of |G | and |G ⊥ |. Coexistence of the non-uniform distortion and of the random phason strain contributes to the ordering process below T c . The diffuse scattering from atomic short-range order (SRO) was distributed around the ideal positions of the superstructure reflections. The SRO diffuse scattering disappeared completely above T c + 10 K. In addition, a small hysteresis of the SRO diffuse scattering was found in the temperature cycle.

Anisotropic local structure of decagonal quasicrystals by DAFS

“…This result suggests that the atomic arrangement becomes almost random far above T c . The temperature dependence of DAFS along the quasiperiodic direction coincides with that of SRO diffuse scattering at the ideal positions of the superstructure [8].…”

“…The specimens used in this study were the same single quasicrystals used in previous studies [8,9]. At each temperature, DAFS data were collected just after the measurement of SRO diffuse scattering.…”

“…At each temperature, DAFS data were collected just after the measurement of SRO diffuse scattering. By in situ observation at high temperature [8], the temperature of an order-disorder phase transition was found to be 992 K (¼T c ). In order to obtain information on the disorder state, we measured SRO diffuse scattering and DAFS far above T c .…”

“…Here, SE is induced by SRO. In Al 72 Ni 20 Co 8 , which has no phasons, pure SRO has been analyzed quantitatively by anomalous X-ray scattering (AXS) [8]. The total SRO diffuse intensity is decomposed into three partial diffuse intensities, which are derived from Al-Ni, Ni-Co and Co-Al pairs.…”

Twenty years of structure research on quasicrystals. Part I. Pentagonal, octagonal, decagonal and dodecagonal quasicrystals

“…The correlation length of the SRO related to the width of diffuse maxima amounts to approximately the % 20 A cluster diameter. In another experiment the diffuse scattering of annealed (1073 K, 1 d) d-Al 72 Co 8 Ni 20 was studied in situ in the temperature range 965 T 1116 K (Abe, Saitoh, Ueno, Nakao, Matsuo, Ohshima, Matsumoto, 2003). The quenched (from 1073 K) sample shows diffuse peaks at the locations of S1 superstructure reflections, which become sharper at 965 K and disappear at 1002 K (¼ T c þ 10 K).…”