HAL Id: jpa-00217597
https://hal.archives-ouvertes.fr/jpa-00217597
Submitted on 1 Jan 1978
HAL is a multi-disciplinary open access
archive for the deposit and dissemination of
sci-entific research documents, whether they are
pub-lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d’enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.
STRUCTURAL TRANSFORMATION STUDIED BY
THERMAL EXPANSION ON SINGLE CRYSTALS
V3Si IN NORMAL AND SUPERCONDUCTING
STATES
T. Fukase, T. Kobayashi, M. Isino, N. Toyota, Y. Muto
To cite this version:
JOURNAL DE PHYSIQUE Colloque C6, supplément au n° 8, Tome 39, août 1978, page C6-406
STRUCTURAL TRANSFORMATION STUDIED BY THERMAL EXPANSION ON SINGLE CRYSTALS
V
3Si IN NORMAL AND SUPERCONDUCTING STATES
T. Fukase, T. Kobayashi, M. Isino, N. Toyota and Y. Muto
The Research Institute for Iron, Steel and Other Metals, Tohoku University, Sendai, 980 Japan
Résumé.- Plusieurs monocristaux de V3Si de pureté différente ont été analysés par dilatomé'trie en présence et en l'absence de champ magnétique. L'anisotropie de dilatation indique que la transforma-tion martensitique commence bien au-dessus de 30 K. Ceci peut s'expliquer par la formatransforma-tion de micro-domaines .
Abstract.- Measurements of the thermal expansion are presented on several single crystals of V3Si with various purities in the absence and presence of magnetic fields. The anisotropic thermal expan-sion indicates that the transformation begins at a temperature above 30 K ; this seems to be explai-ned by the formation of microdomains.
It is well-known that V3Si, one of A15
com-pounds with high T , exhibits a martensitic trans-formation from cubic to tetragonal structure over a range of temperature somewhat above T . According to Fawcett/1/, a large anomaly in thermal expansion coefficient, a, results from the structural trans-formation. We present the thermal expansion data on several single crystals with various resistance ra-tio, R =(P-3f.n/pT £ T ) an<J discuss about the struc-tural transformation and its relation to supercon-ductivity.
As the behaviour of V3Si is sensitive to
strain, two kinds of measuring methods were taken in mounting the samples in the capacitance dilatometer Since only a small part of the sample was subject to the force of about 200 g.wt in the method A, the method B was devised that the weak, homogeneous for-ce is applied over the sample surfafor-ce (See figure 2 ) .
In figure 1 is shown a along [0°Ll a xis mea-sured with increasing temperature for three samples V3Si-5(R=90), V3Si-l(R=17) and V3Si-7-2(R=10). (See
figure 2 on the whole behaviour of V3Si-5). The a
values around T are large for two samples with hi-gher purity, especially extraordinarily large for V3Si-5, in comparison with a at room temperature
of about 7 x 10~6K_1/2/.a jumps large at T with
increasing R. With increasing temperature, a increa-ses steeply above T , attains to a sharp peak at T , and then decreases rapidly up to 30 K and more. The steep increase in a just above T is consistent with [oof] a x^s being the "a" axis in the
tetrago-nal phase. V3Si-5 behaves like the sample A of
Faw-cett/1/. When we destroy superconductivity by field, i of V3Si-l comes on the line extrapolated from
*
Q' V
3Si-5 j
| - - V
3Si-7-2 f \
8 Cooi) U \
§6-
/ \ \
i
4
-
/ IV V
%
A° \ \
0
i
O 20 30
Temperature (K)
Fig. 1 : Thermal expansion coefficient, a, along {oofjaxis for three V3Si single crystals as a func-tion of T, o for V3Si-5(R=90,Tc=17.0), • and A for V3Si-l(R=17,Tc=16.7 K) and t and • for V3Si-7-2
(R=10,TC=16.4 K)o,« and t are measured in zero field and A and D in magnetic fields.
higher temperatures. These results suggest that the structural transformation begins at a pretty higher temperature, accompanies enhanced thermal expansion and attains to T with the largest a. It is also
m
found that the occurence of superconductivity sup-presses the structural transformation. Judging from these considerations and also from our another expe-rimental results/3-4-5/, we conclude that the struc-tural transformation is typical for V3Si-5,
imper-fect for V3Si-l and slight for V3Si-7-2.
Fig. 2 :a along F o g ,
Eig
and
E
1 0 7
axes for VsSi
-5 crystal in the measuring methods A (left) and B
(right). Inlets show schematically principal parts
of methods A and B.
In figure 2 are shown the results of V3Si-5
to the @0g,
Dig
and
directions in both
methods (see inlets). It should be emphasized that
methods A and B give quite different results (con-
trary to sign in a) for the <110> direction. Results
are explained as follows.
Inthe cubic phase, three
<loo> axes are equivalent. In the tetragonal phase,
the domain structure appears without volume change
more than 10-"161. When three kinds of domains occur
equivalently, no change appears in a. In the method
A, the relatively large force of about 200 g.wt is
applied to a small part of the sample, so that most
of the domains arrange to have the "a" axis in the
measuring direction. With decreasing temperature,
the cubic to tetragonal transformation proceeds,
the "a" value becomes smaller, and then'the positive
a should be expected in every measuring directions.
In the method B where the stress to the sample is
weak, the domain structures characteristic of the
sample lead to the negative a.
It is also very important to remark that the
anisotropic behaviour still remains at about 30
K
as can be seen in figure 2 (the method B) but it
does not appear at 70 K. Therefore the occurence of
anisotropy is confined to be somewhere between 30 K
and 70K. The phenomena are explained by the forma-
tion of microdomains form higher temperaturesl7-81.
In addition, the thermal expansion was mea-
sured in magnetic fields. Its temperature dependen-
ce in the field below Hc2 show that remarkable hys-
teresis phenomena were observed for V3Si-1 even
above Tc2. These results should be explained by the
existence of the structural transformation. Similar
Phenomena were found in ultrasonic attenuation near
Tc2 in strong fields/4/. The physical origin of both
phenomena may be ascribed to thermodynamic stability
of the tetragonal domains subjected to an intense
field.
In conclusion, the transformation starts from
a temperature above 30
K by means of the formation
of microdomains. The temperature of sharp peak in
a, Tm, is considered to be close to the temperature
of occurence of the macrodomains.
Valuable discussions with Prof. M. Tahiki are
acknowledged.
References
/I/ Fawcett,E., Phys. Rev. Lett
6
(1971) 829
/2/ Testardi,L.R., Phys. Rev.
(1972) 4342
/3/ Fukase,T., Tachiki,M., Toyota,N. and Muto,Y.,
Solid State Commun.
18
(1976) 505
/ 4 /
