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STRUCTURE AND PHYSICAL PROPERTIES OF A
SIMPLE METAL-METAL AMORPHOUS ALLOY
Mg70Zn30
T. Mizoguchi, N. Shiotani, U. Mizutani, T. Kudo, S. Yamada
To cite this version:
JOURNAL DE PHYSIQUE Col Loque C8, sunple'menl nu n08, Tome 4 1 , aoct 7090, pago C8-183
STRUCTURE AND PHYSICAL
PEOi'EFTIESOF
A
SIMnLE
METAL-METAL
AKORPHOUS ALLOV
F"'p70Zng0x* xxx *XI+ xi**
T. :!izoguchiX, N. Shiotani
,
U. Mizr~tani,
T. Kudo and S. Yamada*
FacuZty o f Science, Gakushitin Ilrziversity, Mejiro, Tokyo 171 ,Japan and L.A. M.S. B . S . ~ l n i v e r s i t 6 Louis Fasteur - 4, rue F l a i s e Pascal 67070 - St;rasbourg Czdex, France.++
The I n s t i t u L e o f Phy:;icaZ and Cherm:caZ Research - k'akoshi, Saitnma 3 5 1 Japan.xrx FacuLty o f Engineering, Nagoya U n i v e r s i t y , Nagoya 4 6 4 Japan.
*xu* Faculty o f Sc-ience, (;akushuin U n i v e r s i t y , i t e j i r o , Tokyo 1 7 1 Japqn.
R6sum6.- La structure atomique et 6lectronique d'un alliage amorphe Mg 7oZna0 simplement diva- lent du type m6tal-mgtal a 6t6 15tudi6e par des mesures de temps de vol en lffraction neutro- nique et par des expgriences d'annihilation de positrons. Le nombre d'onde de coupure 2 k =
F 2.86
A-l
est 16gPrement sup6rieur 5 la valeur de Q (2.62A-')
correspondant au premier pic de la fonction d'interfgrence S(Q). Les mesures de chaleur sp6cifIque 2 basse temp6rature donnent les valeurs de y = 0.940 i 0.009 mJ/mole K' (cf y = 0.92 dans un mod6le d'glectrons libres) et de la tempgraturc dc Debye 8 = 295 + 1 K.Abstract.- Atomic and electronic structure of a simple divalent metal-metal amorphous alloy Mg Zn was studied by TOE neutron diffraction and positron annihilation experiments. The culGof?Owave number 2 k = 2.86
A-'
is a little bit higher than the Q value (2.62R-I)
ofF
the first peak of the interrerenee function S((7). The low-temperature specific heat experi- ment gives y = 0.940 ? 0.009 mJ/mole K 2 (ci y = 0.92 for free electron model) and the Debye
temperature 8 = 295 i I K.
The structure o f a simple divalent metal-metal amorphous alloy Yg7nZn7n was studied by means of TOE pulse neutron diffraction at room temperature. The sample was prepared by rapid quenching from the melt with a single-roller technique.
Overall features of both the observed inter- ference function S(Q) (Fig. I) and the pair corre- lation function g(r) (Fig. 2) agree with those ob- tained in a simulation model with realistic pseudo- potentials by Heimendahl /I/ (histograms in
Fig. I and Fig. 2), although the observed peaks - F i g . :The interference function S(Q) of an amor- phous Mg 10Zn3p observed by TOE neutron are lower than those in the model. We get the diffract~on a room temperature (solid
line) and derived from the model of compu- total coordination number Z 12.0. ter simulation / I / (histogram).
The angular correlation of positron annihi- (Fig. 4) is free-electron-like and not much affec- lation radiations shows the parabolic peak with a ted by structural and constitutional randomness, small broad tail (Fig. 3) which is typical in the smearing of the Fermi cut-off is more impor- free-electron-like metals 121. The Fermi momen- tant than in pure !4g or Al. This may be mainly tum Pf deduced by the Fourier transform of the due to the localization of positron state. angular correlation /3/ is 0.753 a.u., or the The experimental results of the low tempera- Fermi wave number k = 1.43
I-'.
Though the elec-F ture specific heat of amorphous Mg 70Zn30 between
tron momentum density 141, which may be propor- 1.7 K and 4.2 K was well expressed as the sum of tional to (dN/dPZ)/PZ
,
in the amorphous phase a linear and of a cubic terms in the temperatureJOURNAL DE PHYSIQUE
Fig. 2 : The pair correlation function g(r) of an amorphous Mg 79Zn?0 derived from neutron diffraction so ~d line) and that ob- tained from the simulated model / I /
(histogram).
Mg-Zn Amorphous
Fig. 3 : The angular correlation of positron annihilation radiation in an amorphous :4g70Zn30 alloy. P is the Fermi momentum.
f
,
I I 1 +*~l--.*~.'0
1
inau
Fig. 4 : The electron momentum density derived as (dN(PZ)/dPZ)/PZ in an amorphous Mgy0Zn30 alloy
Fig. 5 : The temperature dependence of the elec- trical resistivity p in an amorphous Mg,oZn3g alloy
dependence with y = 0.94 f 0.009 mJ/rnole K~ and the Debye temperature €ID = 295 f 1 K. The obseved
y value is close to the expected value
0.92 rnJ1mole K~ from the free electron gas mo- del.
The electrical resistivity shows broad maximum around SO K and above this, i t decreases with increasing temperature (Fig. 5). The cut-off wave number 2 k = 2.86
A-'
for the scattering ofF
conduction electrons slightly exceeds the peak DO- sition (2.62 A-I), but it occurs at the middle of the slope of the first peak of S(Q) which pro- vides the dominant contribution for the electri- cal resistivity. The negative temperature coeffi- cient of electrical resistivity may be interpre- ted by Ziman's theory.
Acknowlegement :
Theiuthors are grateful to Dr J. Durand for reading the manuscript and for valuable discus- sions.
References
/I/ Von Heimendah1.L.. J. Phys. F : Hetal Phys.
9
(1979) 161.121 Shiotani,N., 0kada.T.. Sakai,N., Seki2awa.H. and Wakoh,S., Proc. 5th Int. Conf. Positron Annihilation (Japan Inst. of Yetals, Sendai,
1979) page 669.
I31 Pattison,?. and Williams,B., Sol. State Comm. 20 (1976) 585.
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