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Submitted on 1 Jan 1978
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THERMAL CONDUCTIVITY OF PERFECT AND DEFORMED LEAD CRYSTALS AT LOW
TEMPERATURES
L. Mezhov, Deglin
To cite this version:
L. Mezhov, Deglin. THERMAL CONDUCTIVITY OF PERFECT AND DEFORMED LEAD CRYS-
TALS AT LOW TEMPERATURES. Journal de Physique Colloques, 1978, 39 (C6), pp.C6-1019-C6-
1020. �10.1051/jphyscol:19786450�. �jpa-00217929�
JOURNAL DE PHYSIQUE Colloque C6, supplément au n° 8, Tome 39, août 1978, page C6-1019
THERMAL CONDUCTIVITY OF PERFECT AND DEFORMED LEAD CRYSTALS AT LOW TEMPERATURES
L.P. Mezhov - Deglin
Institute of Solid State Physios Academy of Sciences USSR, 142432 Chemogolovka, Moscow district, U.S.S.R.
Résumé.- On a estimé les libres parcours des phonons J2™ par des mesures de conduction thermique de cristaux de Pb purs aux températures 7,5 - 0,6 K. Dans un échantillon parfait, à I < 2 K, L est limité par la diffusion des phonons sur la surface du cristal. Dans un cristal déformé tp atteint un maximum à 2 K, puis diminue rapidement dans l'intervalle 2 •*• 1 K et aux températures plus bas- ses dépend faiblement de T. Les résultats présentés peuvent être expliqués par la diffusion réson- nante des phonons thermiques sur les structures de dislocation introduites au cours de déformation de l'échantillon aux basses températures.
Abstract.- Mean free path of phonons &p have been estimated from the measurements of the thermal conductivity of pure Pb crystals at temperatures 7.5 -f 0.6 K. In the perfect sample at T <_ 2 K tp is limited by the phonon scattering at the crystal surface. In the deformed one JL, reaches the ma- ximum at 2 K, quickly decreases in the range 2 •+ 1 K and then it weakly depends on temperature.
The present data may be associated with the resonant scattering of thermal phonons on dislocation structures introduced by sample deformation at low temperatures.
Measurements were made on pure (99.9999 Z) Pb crystals with an average diameter 4 mm prepared by zone refining on high vacuum /l/. The samples were placed on a horizontal support made from stainless steel tube coated with a thin teflon film. One of its end was soldered to the copper finger cooled by liquid helium. Once measurements have been carried out its second end was soldered to a face plane of the support and the thermal conductivity measure- ments were repeated. On cooling from room tempera-
tures to the liquid helium temperatures the sample was strained due to a great difference in thermal
compressions of steel and lead (according to 111 a relative elongation of the sample was 0.3 X).
Curves 1,2 and 3 in figure 1 correspond to the conductivities of the perfect, deformed and an- nealed sample in zero magnetic field ; curves 4 and 5 - to the conductivities of the perfect and defor- med sample in a field 10 % higher than the critical one. In zero field at T £ 4 K the thermal conducti- vity of lead is defined by phonon component J^j . It is seen that at deformation not only the magnitude but also the temperature dependence /jfo have chan- ged : at T £ 2. K in the perfect crystal /Vj ~ T3 (a
P piece of straight line on the curve 1) , in the deformed one "\> T5 in the range 2 C T £ I K and clo- ser to /j\j ~T3 at T < 1 K. Appropriate temperature dependencies of mean free paths of phonons &_ (cur- ves 1 and 2) and electrons (curve 4) are shown in figure 2. The numeration is the same as in the fi-
gure 1.
Fig. 1 :
Decreasing of Ip(T) at U 2 K in the deformed sample may be associated either with a dynamic scat- tering of thermal phonons by mobile dislocations or with a phonon scattering on statistically ordered
22 - T.2
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19786450
nets of dislocations accumulated in slip bands at the crystal plastic deformation. All the other me- chanisms of phonon scattering on lattice defects (point defects, strain fields of isolated disloca- tions, grain boundaries) result in monotonically increasing R (T) dependence or in R (T)=const. 131.
P P
The elastic string m d e l of dynamic phonon scatte- ring /4,5/ requires mean dislocation loop lengths between pinning centers 5 x cm and dislocation density 3 x 10' cm-2 under the condition T % 0.7K
res If phonons scatter on ordered nets of dislocations then the average distance between dislocation walls must be 5 X
lo-'
cm and the characteristic net di- mensions formed by intersecting dislocation loopscm.
The atithor is grateful to. J.V. Iosilevskaya, A.V. Lokhov and V.N. Khlopinski for their partici- pation and help in the experiment.
References
/I/ Mezhov-Deglin, L.P., Kopylov, V.N. Pribory i Technika Experimenta (Russian) NI (1975) 230.
/2/ Corrucini, R.J., Gniewek, J.J., NBS Monograph 29 (1961).
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/ 3 / Ziman, J., Electrons and Phonons (1 960).
141 Garber, J.A., Granato, A.V., J. Phys. Chem.
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