Phase Equilibria in an Ordering Alloy System

Abstract

The equilibria between phases in platinum alloys containing 42, 48, and 54 atomic percent cobalt were determined at temperatures below 1000°C. This system of alloys exhibits an order-disorder transition analogous to that for CuAu. A temperature range in which ordered and disordered phases coexist in equilibrium was determined for each alloy. These data were incorporated in the phase diagram. The Co-Pt system is the first ordering alloy system in which it has been shown that this reaction is a true phase transformation contrary to the prevalent concepts of the phenomena.

Revealing low-temperature atomic ordering in bulk Co-Pt with the high-throughput ab-initio method

“…26 The global convex hull consists of hcp-(Co, D0 19 ) and fcc-structures (b 2 ,Co 2 Pt 7 , Pt 8 Ti, Pt) that appear in the Co-rich and Pt-rich regions, respectively. This correlates with the experimentally observed stability of hcp-Co (at low temperatures) and fcc-Pt, 24,25,27,32 reproduced by our calculations. The deepest global ground states (i.e., those most affecting the shape of the convex hull) are hcp D0 19 The experimental Co-Pt phase diagram includes the CoPt-L1 0 and CoPt 3 -L1 2 structures.…”

“…9,[21][22][23] For Fe-Pt, the experimental (high-temperature) 24,25 and ab-initio (zero-temperature) phase diagrams 26 have been studied extensively. However, in the case of Co-Pt, the experimental characterization is incomplete, 24,25,[27][28][29][30][31][32] and a comprehensive first-principles description has not yet been reported.…”

“…It is known that Co transforms from hcp to fcc at $422 C, 24,25 therefore, it is reasonable to conclude that L1 2 -Co 3 Pt and L1 0 -CoPt could be promoted at higher temperatures, when anharmonic contributions to the vibrational entropy stabilize fcc over hcp like in Co. 24,25,27,32 Their observation at lower temperatures is possible if the fcc/hcp transition is kinetically suppressed. For all temperatures, a competition between L1 2 and D0 23 could exist.…”

Magnetic properties of the ordered VPt3 alloy. I. — Ferromagnetic behaviour

“…The paramagnetic susceptibility x(T) of each VPt3 sample was found to be field independent in the whole temperature range 300 K to 1 100 K, within the experimental error of about 1 %. The paramagnetic behaviour of each VPt3 sample is described with an accuracy better than 5 % in the temperature range 340 K to 1000 K by the modified Curie-Weiss law x(T) = x' + C(T -0)-1, as shown by figure 7. Fig.…”

“…show simple atomically ordered structures. These latter exist at stoichiometry only, or in a given concentration range [1][2][3][4][5][6][7][8][9]. Several of these systems show peculiar physical features, especially from a magnetic view-point, in the ordered state : for example, CrPt3 [10] and MnPt3 [11] show ferromagnetic ordering, although Cr and Mn are antiferromagnetic and Pt is non magnetic, whereas FePt3 shows antiferromagnetic ordering [12].…”