The results of a previous study (1) using Mossbauer resonance spectroscopy have supported the hypothesis of Hume-Rothery (2) in that the order-disorder phenomenon is the result of a non-negligible difference in the electronegativity between the atomic species in presence. In a binary ordered alloy, for example, the A atoms have a tendency to be surrounded by B atoms, and inversely, so as to minimize the Coulomb interaction energy. This tendency is at its maximum when the degree of order is the greatest: due consideration being given to the chemical composition.Such a study has now been applied to the order-disorder transformation in FeNi3:an alloy possessing important applications because of its soft magnetic properties.This investigation has also permitted a comparison of the relative sensitivities of Mossbauer resonance spectroscopy and X-ray diffraction techniques.The iron-nickel alloy was melted and cast in a high-frequency vacuum induction furnace. The finished product -a cylindrical bar 5 cm in diameter -was chemically analysed and found to be free from segregation. The nickel content was found to be 75.35 wt% or 74.45 at%.The cylindrical bar was hot-rolled to a thickness of 12 mm and then cold-rolled, with intermediate heat-treatments to a final thickness of 35 Fm. Final cold-rolling to thicknesses less than 0.1 mm was performed using the sandwich technique.Mossbauer experiments were performed on suitably heat-treated 35 p m thick foils whereas D. S. diffraction patterns using C u K a radiation were obtained from carefully prepared filings subjected to the same heat-treatments.In both cases, the disordered condition was realized by heating the material in a sealed quartz tube containing a residual argon pressure of approximately 150 Torr for 15 min at 1000 C followed by a water quench at 1 5 OC. The ordered condition was obtained by a prolonged heat-treatment in a similar argon atmosphere for a period of two weeks at 450 OC followed by air-cooling of the sealed quartz tube.
A complete theory of the lens-shaped intersection of Kossel lines in the transmission pseudo-Kossel method is developed. The general expression gives the lattice parameter with respect to the characteristics of the interaction of two arbitrary conics, i.e., conics corresponding to arbitrary diffracting planes and arbitrary wavelengths. Geometrical considerations involving the conics are developed and from these, the errors involved in lattice parameter measurement are evaluated. Lattice parameter variations of 10−5 can be easily measured with suitably chosen conic intersections. The precision to be expected as a function of measurement errors is expressed as a sensitivity ratio and tabulated for an Fe-3wt.%Si alloy. Several methods of reducing measured lengths to lattice parameter data are evaluated. The IBM 7090 computer has been used to find suitable intersections for precise lattice parameter measurement. The computer supplies the wavelengths and conics to be used in the transmission pseudo-Kossel method. Consequently, a long and tedious experimental investigation is avoided. Examples using Fe-3wt.% Si are given; the lattice parameter for this alloy is found to be 2.86268±0.00003 Å. Proper radiations for investigation of Ge and diamond are indicated.
A Mossbauer investigation in Fe-A1 alloys ranging from 20 to 28 atyo A1 has been performed. I n the disordered spectra, which were computer analyzed, a very slight mean electric quadrupole interaction has been measured, which may be due to some directional order, while in the ordered spectra two ordered phases were observed for a composition around 25 atyo Al: the DO,-type of ordered structure, in which each A1 atom has eight Fe nearest neighbours and six Fe next-nearest neighbours, and another phaEe with a structure similar to Cu,Au, in which each A1 atom has 12 Fe nearest neighbours and six A1 next-nearest neighbours. Both phases are ferromagnetic. I n the Cu,Au-type structure a strong electric quadrupole interaction has been measured, which is the same as in the Fe,AIC compound. The quadrupole effect does not appear in the DO,-type structure probably because of special relationships between the easy axis of magnetization and the electric field gradient tensor. Measurements of quadrupole effects show that A1 should be strongly ionized when alloyed with Fe. This gives a clue to understand the physical reasons why order-disorder transitions appear in such alloys. Below the transition temperature, each A1 gets better surrounded exclusively by Fe atoms in order to minimize the Coulomb interaction energy with its neighbours.I n Fe-A1 -Legierungen mit 20 bis 28 atyo A1 wurde eine MoBbaueruntersuchung durchgefuhrt. I n den Fehlerordnungsspektren, die maschinell analysiert wurden, wird eine sehr leichte, mittlere, elektrische Quadrupolwechselwirkung gemessen, die durch eine Richtungsordnung hervorgerufen sein kann, wahrend in den Ordnungsspektren zwei geordnete Phasen fur eine Zusamniensetzung um 25 atyo A1 beobachtet wurden: der DO,-Typ der geordneten Struktur, in dem jedes Al-Atom acht nachste Fe-Nachbarn und sechs iiberniichsteFe-Nachbarn besitzt, und eine andere Phase mit einer iihnlichen Struktur wie Cu,Au, in der jedes Al-Atom 12 nachste Fe-Nachbarn und sechs ubernachste Al-Nachbarn hat. Beide Phasen sind ferromagnetisch. I n der Struktur vom Cu,Au-Typ wurde eine starke elektrische Quadrupolwechselwirkung gemessen, die dieselbe wie in den Fe,Al-Verbindungen ist. Der Quadrupoleffekt tritt nicht in der DO,-Struktur auf, wahrscheinlich wegen der speziellen Beziehungen zwischen der leichten Magnetisierungsachse und dem Tensor des elektrischen Feldgradienten. Messungen des Quadrupoleffekts zeigen, daB A1 in der Legierung mit Fe stark ionisiert sein sollte. Dies ergibt einen Anhaltspunkt. die physikalilischen Grunde zu verstehen, warum Ordnungs-Fehlordnungsubergange in solchen Legierungen auftreten. Unterhalb der tfbergangstemperatur wird jedes Al-Atom immer besser ausschlieIlich von Fe-Atomen umgeben, um die Coulombwechselwirkungsenergie mit seinen Nachbarn zu minimalisieren.
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