Electronic Properties and Stability of the TiAl 3 and MoPt 2 Type Ordered Structures in Binary Transition Metal Alloys
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ELECTRONIC PROPERTIES AND STABILITY OF THE TiAl STRUCTURES IN BINARY TRANSITION METAL ALLOYS
3
AND MoPt
2
TYPE ORDERED
AND A. BIEBER, P. TUREK, R.M. WATERSTRAT, C.N.R.S., L.A. 306, Institut de Physique, 67084 Strasbourg, France ; * N.B.S. Washington, D.C. 20234, U.S.A. ;*3 C.R.M., C.N.R.S., 6, rue Boussingault, 67083 Strasbourg, France R.
KUENTZLER,
* L.M.S.E.S.,
ABSTRACT In view of the recent constitution diagrams (for binary transition metal alloys) a systematic study of the electronic properties of all alloys which have either the TiAI 3 or MoPt 2 type of structure has been undertaken. Specific heat results are reported and briefly discussed in the frame of the theoretical calculations about band structure and stability of ordered alloys.
INTRODUCTION A large effort has been pursued on the formation of disordered alloys by empirical and theoretical developments based on the electronic structure of the alloys. The problem of ordered alloys has been much less studied both from an experimental and theoretical viewpoint up to recently. The situation was complicated by the lack of detailed experimental informations about the constitution diagrams and consequently very few physical studies were available. Recent developments both in statistical calculations of phase diagrams [13 and in the study of stability of ordered structures, based on the electronic structure of the alloys [fJ, have been reported. The simultaneous progress registered in the determination of experimental constitution diagrams [31 stimulated studies of the physical properties of ordered alloys and in particular on their electronic properties [4, 5]. Therefore we have started some years ago an experimental program [41 on ordered binary transition metal alloys AcBIc in order to obtain informations on the electronic properties and to find out whether some empirical rules previously observed [61 are general and can be interpreted in view of the theoretical developments presently in progress. Here we consider the case of binary transition metal alloys which have a TiAI 3 or MoPt 2 type ordered structures and present original experimental results on the electronic specific heat which yield the density states at the Fermi level of ordered alloys. CONSTITUTION DIAGRAMS AND SAMPLE PREPARATION Constitution Diagrams Most of the phase diagrams with which we are concerned have been recently investigated. This is in particular the case for V-Pt, Nb-Pd, Ta-Pd, Nb-Pt[7-10].However the case of Ta-Pt will not be considered here since this incompletely known and the structure of TaPt 2 is not yet diagram is still well established. The formation of the ordered alloys of the TiAI3-type and MoPt 2 -type structures is obtained through various types of reactions : (1) standard order-disorder transformations from an f.c.c. solid solution, this is the case for VNi 3 , VNi 2 , VPd 3 , VPd2, VPt 3 , VPt 2 and MoPt 2 . The case of NbPd3 is special since it is formed by a congruent order-disorder transformation, (2) congruent melting, TaPd 3 and TaPd 2 and (3) formatio
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