In the present study experimental data available in the literature have been
employed to investigate behavior of the critical temperature Tc as a function of the
pressure P, in the YBa2Cu3O6+x high temperature superconductor (HTSC). We
estimated the maximal critical temperature Tc,max(P) which can be achieved in this
material under pressure applied at temperatures low enough to prevent oxygen
reordering. We found that it approximately equals to 114K corresponding to x ≈
0.77

Milić, Mirjana M.

Repository of the Vinča Nuclear Institute (VinaR)

       PHYSICAL CHEMISTRY 2010  10th International Conference on Fundamental and Applied Aspects of Physical Chemistry  Proceedings      The Conference is dedicated to the 100th Anniversary of the academician Pavle Savić birthday and 20th Anniversary of the Society of Physical Chemists of Serbia         21-24 September 2010 B E L G R A D E                            ISBN 978-86-82475-17-0 Title: Physical Chemistry 2010. (Proceedings) Editors: S. Anić and Ž. Čupić Published by: Society of Physical Chemists of Serbia, Studentski trg 12-16 P.O.Box 47, 11158 Beograd, 218, Srbija Publisher: Society of Physical Chemists of Serbia For Publisher: S. Anić, President of Society of Physical Chemists of Serbia Printed by: “Jovan” Printing and Publishing Company; 200 Copies; Number of pages 16 + 388, Format: B5; Printing finished in September 2010.  Text and Layout: “Jovan”  200 - Copy printing    II   The Society of Physical Chemists of Serbia  in co-operation with   Institute of Catalysis, Bulgarian Academy of Sciences  Boreskov Institute of Catalysis, Siberian Branch of  the Russian Academy of Sciences  Faculty of Physical Chemistry, University of Belgrade, Serbia  Institute of Chemistry Technology and Metallurgy, University of Belgrade, Serbia  Vinča Institute, University of Belgrade, Serbia   Institute of General and Physical Chemistry, Serbia                         IV  International Organizing Committee  Chairman:             S. Anić (Serbia) Vice-chairman:     N. Stepanov (Russia)                                B. Adnađević (Serbia)  Members: M. Gabrovska (Bulgaria), N. Cvijetićanin (Serbia), T. Grozdić (Serbia),  D. Jovanović (Serbia), M. Lalić (BiH), D. Marković (Serbia), B. Milosavljević (USA), N. Miljević (Serbia), M. Mojović (Serbia), N. Ostrovski (Serbia), C. Pona (Italy), B. Simonović (Serbia), D. Stanisavljev (Serbia), A. G. Stepanov (Russia), V. Vasić (Serbia), N. Vukelić (Serbia), V. Vukojević (Sweden)   International Scientific Committee  Chairman:              Ž. Čupić (Serbia) Vice-chairmans:     V. N. Parmon (Russia)                                 M. Franko (Slovenia)  V. Vasić (Serbia)  Members: A. Antić-Jovanović (Serbia), G. Bačic (Serbia), R. Cervellati (Italy), R. Compton (United Kingdom), V. Gaspar (Hungary),  M. Jeremić (Serbia), A. L. Kawczyñski (Poland), Lj. Kolar-Anić (Serbia), S. Kuchanov (Russia), R. Leblanc (USA),  S. Mentus (Serbia), S. Milonjić (Serbia), Lj. Morozova-Roche (Sweden),  D. Moscone (Italy), J. Nedeljković (Serbia), Z. Noszticzius (Hungary), M. Perić (Serbia), V. Petruševski (Macedonia), M. Plavšić (Serbia), G. Smulevich (Italy),  G. Schmitz (Belgium), I. Schreiber (Czech), P. Ševčik (Slovakia), N. Stepanov (Russia), M. Trtica (Serbia), D. Veselinović (Serbia)  Local Executive Committee  Chairman:              B. Adnadjević Vice-chairmans:    S. Blagojević                                 A. Ivanović  Members: A. Abu Rabi-Stanković, P. Banković, N. Begović, S. N. Blagojević,  N. Cvjetičanin, M. Daković, A. Đerić, A. Ignjatović, Lj. Ignjatović, A. Jović,  J. Krstić, S. Kuprešak, D. Lončarević, J. Maksimović, V. Marković, M. Milenković, M. Milojević, Z. Mojović, B. Nedić, I. Pašti, N. Pejić, A. Popović-Bjelić, M. Petković, N. Potkonjak, D. Ranković, R. Ranković, M. Stević,  I. Stojković, B. Šljukić, M. Vujković    VSTUDY ON THE DEPENDENCE OF THE CRITICAL TEMPERATURE Tc ON PRESSURE IN YBa2Cu3O6+x  M. M. Milić  Laboratory of Theoretical Physics, INN Vinča, P.O.Box 522, 11001 Belgrade, Serbia  Abstract In the present study experimental data available in the literature have been employed to investigate behavior of the critical temperature Tc as a function of the pressure P, in the YBa2Cu3O6+x high temperature superconductor (HTSC). We estimated the maximal critical temperature Tc,max(P) which can be achieved in this material under pressure applied at temperatures low enough to prevent oxygen reordering. We found that it approximately equals to 114K corresponding to x ≈ 0.77.  Introduction Many studies conducted in the past years on the pressure effect in HTSC materials revealed the complex nature of the pressure dependence of Tc in these materials, since Tc depends on many different parameters such as hole carrier density, interplanar and intra planar spacing, relaxation parameters etc. [1,2]. It is usually assumed that two different terms contribute to the pressure coefficient (dTc/dp), one, which results from the pressure induced charge transfer and the other, intrinsic one, which is not result of the charge transfer [3]. For the HTSC compounds with initially positive pressure coefficient, it is characteristic that the pressure increase leads to the enhancement of the Tc until, for some pressure Pmax, the maximum Tc is reached, and at yet higher pressures Tc decreases again [4]. In YBa2Cu3O6+x material pressure coefficient considerably depends on the oxygen concentration x. For x ≈ 0.97 the material is optimally doped and the pressure effect is almost negligible. For very under doped samples a giant pressure coefficients up to 30K/GPa was reported when the pressure was applied at room temperatures, while at 100K only moderate Tc increase was achieved (2-4K/GPa) [5]. The Tc enhancement at room Fig.1. Tc as a function of pressure P for different oxygen concentrations x. The results are reproduced from the Ref. [4]. 467temperature was attributed to the increased doping of CuO2 planes achieved by the pressure induced oxygen reordering which is suppressed at low temperatures [5].  Results and discussion Since the pressure application increases number of holes in the CuO2 planes, there is a certain similarity between doping and pressure experiments. Therefore, the following relation is able to describe the Tc vs P behavior observed in many high-Tc cuprates [6]: ( 2,max max( ) 1c cT P T A P P )⎡ ⎤= − −⎣ ⎦ .    (1) In the present paper we have employed this relation to fit the experimental results of Sadewasser et al [4] who have measured the critical temperature Tc as a function of the hydrostatic pressure P, in YBa2Cu3O6+x over the wide range of oxygen concentrations x (figure 1) at temperatures which exclude the oxygen reordering. Then we presented the so obtained Tc values as a function of the concentration x at different P = const values, and fitted those Tc(x) dependences to the parabolic curve as shown in the figure 2. Such an approximation was suggested by Stankowski et al [6] and it can be seen that the Tc(x) values extracted from (1) for P = const are fitted by the parabolic approximation very well. However, we must note that it is not strictly valid in the whole range of oxygen concentrations since it does not includes 60K plateau displayed in the Tc vs. x characteristic at P = 0  for 0.5 < x< 0.63(3). From the fig. 2 (we showed the results only for two values of P ≠ 0) it can be seen that with the pressure increase leads to the higher maximal Tc value and that it is achieved for samples with lower oxygen concentration x. This implies that at high pressures the optimal hole doping of CuO2 planes is achieved for the samples with larger oxygen deficiency, such a behavior being the obvious consequence of the additional pressure induced charge transfer from CuO to the CuO2 planes. The paraboFig. 2. Tc as a function of the oxygen content x at P=0 and under pressure for P=5GPa and P=8GPa. The lines are parabolic approximation to the experimental results taken from [3]. lic approximation of the existing experimental results for Tc(x) dependence at high constant pressures enabled determination of the Tc(P) dependences for the samples in the wide range of oxygen concentrations where  experimental results are available. For those samples, which do not reach their 468maximal Tc values for pressures that are too high, the equation (1) is used to determine their maximal Tc under pressure. We presented this way estimated maximal Tc values as well as those determined  experimentally a function of the concentration x in the figure 3. We found that this dependence can be also, to a very good approximation fitted to the parabolic curve. This way the maximal Tc under pressure, can be determined for the whole range of concentrations x where the material behaves as a superconductor.  Conclusion We estimated the maximum Tc, at can be achieved under w temperatures in ted by the Ministry of Science of the Republic of Serbia ling, Treatise on High Temperature Superconductivity, ed. by J. R. conducting materials, Springer Berlin merman, Phys. Rev. B, 1993, 47, 8385. Rev. B, 2000, etz, R. Quenzel, H. A.Ludwig, K. Grube, S. I. Schlachter, F. W. Stankowski, M. Krupski, R. Micnas, Mater. Sci. Poland, 2004, 22, 175-185. thpressure at loYBa2Cu3O6+x HTSC, to be approximately 114K, and it is reached for x ≈ 0.77, which is the concentration close to the one at which the maximal pressure coefficient is measured [5]. However, it was not possible to determine the value of the pressure at which this maximum Tc is reached, though our analyses indicate that it is around 9GPa. For more precise estimation, high pressure experimental results for Tc obtained on the larger set of samples with different oxygen contents are needed.  cknowledgement Fig. 3. Maximal Tc which can be achieved in the sample under pressure as a function of the concentration x. AThis work was supporthrough the project No. 141014.   References[1] J. S. SchilSchrieffer, Springer, Verlag, 2006, 427-462. [2] B. Lorenz, C. W. Chu, Frontiers in superHeidelberg, 2005, 459-497. [3] J. J. Neumeier, H. A. Zim[4] S. Sadewasser, J. S. Schilling, A. P. Paulikas, B. W. Veal, Phys. 61, 741-749. [5] W. H. FiHornung, T. Wolf, A. Erb, M. Klaser, G. Muller-Vogt, Physica C, 1996, 270, 258-266. [6] J. 469

Study on the dependence of the critical temperature Tc on pressure in YBa2Cu3O6+x

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Study on the dependence of the critical temperature Tc on pressure in YBa2Cu3O6+x

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