Thermal properties of swift heavy ion irradiated CuO

doi:10.1016/S0168-583X(99)00264-5

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

Volume 156, Issues 1–4, 2 July 1999, Pages 222-226

https://doi.org/10.1016/S0168-583X(99)00264-5 Get rights and content

Abstract

Thermal properties of swift heavy ion irradiated CuO has been studied using the photopyroelectric (PPE) technique. We have observed changes in the thermal properties of irradiated CuO due to out-diffusion of oxygen. These changes take place slowly while the samples are in vacuum during measurements.

Introduction

Study of the thermal conductivity and the specific heat of condensed materials are important from both basic as well as application point of view. It is interesting to note that the order of magnitude of the thermal conductivity (k) of the high temperature superconductor (HTSC) [1] and colossal magneto resistance (CMR) ceramic oxides [2] is similar to the k of amorphous silicon dioxide (a-SiO₂, k < 5 W/mK) [3] near room temperature. The electrical conductivity (σ) of HTSC (YBa₂Cu₃O_6.9, σ ≈ 10³ Ω⁻¹ cm⁻¹) and CMR oxides (La_0.85Sr_0.5MnO₃, σ ≈ 50 Ω⁻¹ cm⁻¹) are in the metal-semiconducting range at room temperature, however k is of the order of the thermal insulators.

Variation in the thermal properties of high T_c cuprate superconductors after irradiation with heavy ions is getting attention of many groups. Study of thermal properties of irradiated HTSCs is important to understand the dissipation of heat from any device fabricated using the irradiated samples. Moreover, the study of the effects of oxygen vacancy defects and ion-irradiation induced structural defects in the HTSCs is essential in order to understand the details on how these defects are formed and each defect type alters the transport and magnetic properties in these materials. Our aim is to study the thermal properties of CuO before and after irradiation with high energy heavy ions. Irradiation of samples is carried out in the high vacuum conditions. Large amount of energy deposited along the track of the bombarding particles (≅keV/°A) will give deformations in the structure of the sample as well as loss of oxygen from the irradiated volume of the CuO pellet. It is expected that the ambient will change the physical properties of the irradiated sample as soon as it is out of the high vacuum chamber. In this work, our initial observations about the changes in thermal properties due to the effect of exposing the sample to air on an irradiated CuO pellet are reported.

The photopyroelectric (PPE) technique has been used to study the thermal properties of CuO. The usefulness of the PPE technique to measure specific heat (C), thermal conductivity (k) and thermal diffusivity (D) of the condensed phases have been shown [4]. In the PPE technique, thermal waves are generated in the sample by the absorption of chopped or pulsed light and these thermal waves are detected by a pyrosensor sitting adjacent to the sample. Periodic variation of the voltage (V) and phase (φ) across the pyrosensor due to thermal waves are detected. Knowledge of V and φ as a function of chopping frequency (f) is necessary to calculate the values of C and k. Detailed functional relation among C, k, V, φ and f have been worked out by Mandelis and Zver [5].

Section snippets

Experiment

Details about the sample preparation has been published earlier [6]. The pellet of CuO was irradiated with a fluence of 4 × 10¹³ ions/cm² of 100 MeV Ag ions at 15 UD Pelletron of Nuclear Science Centre, New Delhi. The sample was tilted at an angle of 30° with respect to the beam direction to carry out on-line elastic recoil detection (ERD) measurement during irradiation.

Experimental details of the PPE set-up used in the present study have been reported earlier [7]. Chopped light from a 2 mW HeNe

Results and discussion

Variation of V and φ as a function of f in the states A and B of the irradiated CuO pellet are shown in Fig. 1, Fig. 2 at 300 and 100 K, respectively. Experimental results during the states A and B of the sample are shown by open and closed symbols respectively. There is very small difference in the results of the states A and B at 300 K (Fig. 1). On the other hand it is quite large at 100 K (Fig. 2). After measurements in the state B of the sample, air was introduced in the cryostat at 300 K

Conclusions

Thermal properties of swift heavy ion irradiated CuO has been studied using the PPE technique. Changes in the thermal properties of irradiated CuO can be possibly attributed to the out-diffusion of oxygen. The changes take place slowly when the samples are in vacuum while carrying out the measurements.

Acknowledgements

One of the authors (PS) wishes to thank the CSIR, New Delhi for the award of Research Associateship.

References (11)

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