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Optical Properties of NiAl Intermetallic Compounds during Concentration and Temperature B.C.C.–F.C.T. Transitions
Author(s) -
Sasovskaya I. I.,
Korabel V. P.,
Shreder E. I.
Publication year - 1985
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2221290226
Subject(s) - nial , intermetallic , materials science , absorption (acoustics) , phase (matter) , phase boundary , electronic band structure , crystallography , condensed matter physics , electron , analytical chemistry (journal) , chemistry , physics , alloy , metallurgy , quantum mechanics , organic chemistry , composite material , chromatography
Optical constants in the spectral interval ħ ω = 0.07 to 4.7 eV are measured to investigate the electronic structure of the b.c.c. β′‐phase (type B2) of NiAl compounds over the entire range of the β′‐phase and especially at the boundary of the β′‐phase, when the latter changes into a lowersymmetry f.c.t. (type LI 0 ) phase. The behaviour of the special features of the optical absorption can be explained, if it is assumed that with the growth of Ni content the Ni d‐band terminates on E F , so that E F is at the small density‐of‐states peak. This is the cause of the structural instability of NiAl compounds in the vicinity of 60 at% Ni. Following the b.c.c.‐f.c.t. martensite transformation the higher‐energy (ħ ω > 3.5 eV) optical absorption structures due to electron transitions not including E F , are conserved, while the low‐energy structures (ħ ω < 3.5 eV) disappear and a new absorption band emerges in their place in the infrared region of the spectrum at ≈ 0.8 eV. These changes are analyzed using a Jahn‐Teller type effect model for the suppression of degeneracy of some electron energy bands at E F . Optical data are in agreement with the similar model of peak N ( E F ) in the b.c.c. phase and N ( E F ) minimum in the f.c.t. phase, proposed earlier.