Negative temperature coefficient of resistivity in samples of Nb 3Ge irradiated by electrons or heavy ions F. Rullier-Albenque, L. Zuppiroli, F. Weiss To cite this version: F. Rullier-Albenque, L. Zuppiroli, F. Weiss. Negative temperature coefficient of resistivity in samples of Nb 3Ge irradiated by electrons or heavy ions. Journal de Physique, 1984, 45 (10), pp.1689-1698. 10.1051/jphys:0198400450100168900. jpa-00209910 HAL Id: jpa-00209910 https://hal.archives-ouvertes.fr/jpa-00209910 Submitted on 1 Jan 1984 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. J. Physique 45 (1984) 1689-1698 OCTOBRE 1984, 1689 Classification Physics Abstracts 61.80F201361.80J201372.15E Negative temperature coefficient of resistivity in samples of Nb3Ge irradiated by electrons or heavy ions F. Rullier-Albenque, L. Zuppiroli Section d’Etude des Solides Irradiés, Centre d’Etudes Nucléaires, B.P. n° 6, 92260 Fontenay-aux-Roses, France and F. Weiss Laboratoire des Matériaux, ENSIEG, ER 155, B.P. 46, 38402 St Martin d’Hères, France (Reçu le 2 décembre 1983, révisé le 4 avril 1984, accepté le 21 juin 1984) Résumé. 2014 Des échantillons de Nb3Ge ont été irradiés à basse température (T~ 20 K) par deux projectiles aussi violemment différents que des électrons de 2,5 MeV et des ions lourds d’environ 100 MeV (fragments de fission de l’uranium). La résistivité a été mesurée en fonction de la température avant et après irradiation. Pour les deux types de particules des valeurs négatives du coefficient de résistivité avec la température d03C1/dT sont mesurées et corrélées à la résistivité résiduelle. Ces propriétés de transport anormales sont discutées et comparées aux résultats des récentes théories consacrées à ce sujet. Qualitativement, il semble clair que, s’agissant d’un système où le libre parcours des électrons est de l’ordre de la distance interatomique, le changement de signe du coefficient d03C1/dT est relié à un processus de localisation des électrons avec la participation d’interactions électron-phonon et électron-électron. En d’autres termes, l’ecart entre les valeurs expérimentales et la théorie de Boltzmann du trans- port dans un gaz d’électrons presque libres est dû à l’interférence entre les collisions sur les impuretés, les collisions électron-phonon et (ou) les collisions électron-électron. Alors que la théorie de Belitz et Schirmacher sur l’effet tunnel induit par les défauts dans les métaux très désordonnés semble la plus appropriée pour expliquer les résultats d’irradiation aux ions lourds, bien qu’elle n’inclue que les interactions électron-phonon, les résultats des irra- diations aux électrons révèlent la nécessité d’inclure les interactions coulombiennes comme dans le modèle de Alts’huler et Aronov. Abstract. 2014 Nb3Ge samples have been irradiated at low temperature (T ~ 20 K) by two drastically different irradiation projectiles : 2.5 MeV electrons and ~ 100 MeV heavy ions (uranium fission fragments). The resistivity has been measured versus temperature before and after these irradiations. For both projectiles negative temperature coefficients of resistivity d03C1/dT were measured and correlated with the residual resistivity p. These anomalous trans- port properties are discussed and compared to the results of the recent theories on the subject. It is qualitatively clear that the change of sign of the temperature coefficient of resistivity, occurring in a system where the electronic mean free path is of the order of the atomic distance, is indeed related to some localization process, helped by electron-phonon and electron-electron interactions. In other words, the deviation of the resistivity from the Boltz- mann nearly free electron behaviour is due to some interference effect between impurity scattering and electron- phonon and/or electron-electron scattering. While the theory of defect induced tunnelling in strongly disordered metals developed by Belitz and Schirmacher seems to be the most appropriate for the explanation of the heavy ion irradiation results, although it includes electron-phonon interactions only, electron irradiation results reveal the necessity of including the interplay with Coulomb interactions as in the model of Alt’shuler and Aronov. 1. Introduction. superconducting transition temperatures. Secondly, they exhibit anomalies in various normal state pro- There has been a great deal of interest in the A-15 perties. In particular, the fact that the A-15 resistivities compounds such as V3Si, Nb3Sn or Nb3Ge because do not increase linearly with temperature and struc- of their various peculiar properties. First of all, tural damage but rather tend to saturate at about they are among the compounds with the highest 120 to 160 u.cm, corresponding roughly to a mean Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphys:0198400450100168900 1690 free path I of the order of the interatomic distance a, 2. Experiments. has attracted considerable attention [1, 2]. The disordered character of these alloys is also reflected 2.1 SAMPLES. - All the Nb3Ge samples used in this in the breakdown of Matthiessen’s rule, the tempe- work have been prepared by chemical vapour depo- sition. The elaboration techniques are described in rature coefficient of dp resistivity (TCR) dT becoming detail elsewhere [8, 9]. Except for one (Nb3Ge-9) the films thickness from 1.5 to 4.5 even negative at low temperatures for sufficiently Nb3Ge (of J.1m) are on 300 thick substrate. disordered samples [3, 4]. This last point appears to deposited J.1m sapphire be quite universal as emphasized by Mooij who The resistivities of these samples were measured by a standard four points method. The estimated error found such correlations between and the resisti- dlnpdT in the absolute values of resistivity is about 20 % due to an of the vity p for a large class of materials [5]. The critical primarily imprecise knowledge value of resistivity beyond which the TCR becomes sample thickness. For the last sample (Nb3Ge-9) are made on both sides of a steel foil negative at room temperature was found by Mooij depositions [9]. In this the is about 20 to be approximatively 150 uQ . cm. It is striking to case, sample tim thick. This small thickness is for electron notice that this value is precisely the one we have relatively very helpful mentioned for the A-15 saturation resistivity. irradiation because high electron beam current can then be used without producing important heating Presently the A-15 superconductor with the highest of the sample. On the other hand the resistivity transition temperature, Nb3Ge, is prepared by sputter- determination is more difficult. At each measurement ing, coevaporation or chemical vapour deposition. point, we have to measure both the resistance of the These elaboration methods allow the A-15 Nb3Ge Nb3Ge-9 sample (Nb3Ge on steel) and the resis- metastable phase to be stabilized and provides films tance of a steel sample of the same nature. In this way with transition temperatures which can reach 23 K. we were able to obtain the absolute Nb3Ge resistivity The transition temperatures, Tc, residual resistivities with an estimated error of 40 %. and temperature coefficients have been shown to be The initial sample specifications are given in table I. strongly correlated to each other and to all depend The different critical temperature Tc and resistivity p on the global degree of disorder of the material [3, 4, 6]. (25 K) values are the results of different growth condi- But the precise nature of this disorder is not at present tions. clear. One may wonder if the disorder is concentrated mainly at the atomic scale such as disorder in amor- 2. 2 IRRADIATIONS. phous alloys (metallic glasses) or if it is related to an 2. 2 .1 Electrons. - The electron irradiation has been inhomogeneity of any kind which could depend on carried out in the Vinkac low the « metallurgical )) qualities of the films. In the temperature facility. This described elsewhere consists of a present paper we try to discuss this problem in device, [10], liquid to a Van der Graaff connection with a set of new radiation damage hydrogen cryogenerator coupled irradiation between 18 and 25 K. experiments in Nb3Ge films. We have tried to change accelerator, allowing the level and the spatial distribution of damage by In addition, it is possible to isolate the irradiation from the and to warm the using two kinds of very different irradiation projec- cryostat cryogenerator up tiles : 2.5 MeV fast electrons which produce mainly sample by a linear increase of the temperature between isolated point defects and ~ 100 MeV heavy ions 20 to 300 K with heating rates from 0.1 to 10 Kelvin minute. The and a steel sam- (uranium fission fragments) which deposit high energy per sample Nb3Ge-9 densities in the form of electronic excitation and ple were irradiated together with 2.5 MeV electrons atomic collisions. Studies of the effects of electron, up to a dose of 4 x 102° e/CM2 corresponding to an electron flux of about 5 x 1014 The irradia- neutron, a-particle and heavy-ion irradiation on the e/cm2/s. electrical resistivity have been reported by other tion temperature never increased above 22 K. The investigators [3, 4, 6, 7]. One of the originalities of sample resistivity was measured continuously during irradiation. After irradiation the irradia- the present work lies in irradiating the same material given times, tions were and the versus tem- by projectiles which are expected to produce very interrupted resistivity different damage distributions.