Identification of low coefficient of thermal expansion in Al23Ce4Ni6 via combinatorial sputtering of Al-Ce-Ni-Mn thin films and upscaling to bulk materials

Abstract

Al100−x-y-zCexNiyMnz thin films were synthesized via combinatorial sputtering from Al, Al80Ce20, Al91Ni9, and Al93Mn7 targets. The resultant as-deposited films exhibit a continuous composition gradient of the various constituents and form a metastable solid-solution over most of the composition space. Subsequent annealing leads to the formation of the thermodynamically stable systems of Al, and α-Al11Ce3, Al8CeMn4, and Al23Ce4Ni6 intermetallics -- where the phases present and fraction depend on the composition. Temperature dependent x-ray diffraction (TDXRD) was used to determine the coefficients of thermal expansion (CTE) for each phase. The thin film Al and Al11Ce3 temperature dependent CTE values are consistent with previously reported results. The thin film Al8CeMn4 phase reveals a slight decrease in the CTE with a range from 27 × 10−6 oC−1 to 23 × 10−6 oC−1 in the temperature range 25–550 °C. The thin film Al23Ce4Ni6 phase exhibits a CTE value of ≈ 9 × 10−6 oC−1 near room temperature and increases to 14 × 10−6 oC−1 at 550 °C. To confirm the thin film results, bulk stoichiometric Al8CeMn4 and Al23Ce4Ni6 samples were prepared and measured under similar conditions. The Al8CeMn4 bulk sample confirmed the negative CTE trend observed in the thin film sample. Compared to its thin-film counterpart, the Al23Ce4Ni6 bulk sample similarly demonstrated a low CTE value near room temperature of 5 × 10−6 oC−1 and an anomalous minimum in the CTE at ≈ 75 °C, which was confirmed via temperature dependent neutron diffraction. Temperature dependent magnetic and electrical measurements were subsequently taken on Al23Ce4Ni6, and the anomalous minimum in the CTE coincided with an electronic phase transition.