Results

1. For experiments carried out in A.F.Ioffe PTI of RAS and Atomic Institute of Austrian Universities the following physical models are developed:
   a) model of an oxygen subsystem of thin films YBaCuO, consisting from microcrystalline of a micron size, subjected to gamma-irradiation [1,2];
   b) model of point defects evolution in YBaCuO singlecrystals subjected to neutron irradiation and consequent annealing [3-6].

2. For thin films YBaCuO, irradiated by various dozes of gamma-irradiation:
   a) the defect distributions formed in oxygen subsystem during gamma irradiation have been calculated on the base of proposed model
   b) resistance vs temperature dependences R(T) (for low temperatures) of YBaCuO films have been obtained using calculated defect concentrations; these dependences have a satisfactory agreement with experimental results. [1,2]

3. The distributions of point defects and their clusterss in oxygen and copper subsystems of YBaCuO singlecrystals subjected to neutron irradiation and annealing have been obtained [3-6].

4. It is shown that for small dozes of a neutron irradiation in YBaCuO singlecrystals:
   a) the critical current density Jc is proportional to average total concentration of pinning centres < C(r) > for low magnetic fields parallel to ab-plane [3,5].
   b) critical temperature of superconducting transition Tc is proportional to relative concentration of oxygen in Cu-O chains for low variations Tc near to initial value [4-6].

5. The numerical values of the following kinetic parameters of YBaCuO [1-3,5] have been obtained: - cross section for oxygen vacancy formation f by ionization for gamma - irradiatione (3 *10^-19 cm²); - sink strength of twin boundaries in the films S = 9*10¹⁰ cm^-2; - bonding energy of oxygen with grain boundaries (1.5eV); - dissociation energy of oxygen (E = 1.5 eV) and copper-oxygen clusterss (E = 1.9 eV); - activation energy of interstitial oxygen migration ab-plane (E_mi = 0.8eV).

Publications

1. D.V.Kulikov, R.A. Suris, Yu.V. Trushin, Physical model of the oxygen subsystem in YBaCuO during gamma irradiation, Phys.Solid State v.36 N10 October 1994 pp.1583-1589
   
   A theoretical investigation is made of the influence of processes taking place in the oxygen subsystem of thin YBaCuO films under the influence of gamma irradiation on the value of crytical temperature of superconducting transition and the dependence of the resistivity on the temperature. Estimates of the numerical values are obtained for the following parameters of oxygen subsystem of thin YBaCuO films: the sink strength, the energy of binding of the oxygen to a sink, and the cross section for the formation of an oxygen vacancy by ionization during gamma irradiation.

2. D.V. Kulikov, R.A. Suris, J.V. Trushin. A model of interaction of oxygen subsistem with intercristallitte boundaries in polycristalline YBaCuO film under gamma-irradiation. Supercond. Sci. & Tehn., v.8, p.303, 1995
   
   The influence of processes occuring in the oxygen subsystem of YBaCuO thin films under gamma-irradiation on the critical temperature and on the temperature dependence of the film resistance has been investigated theoretically. The values of parameters such as sink strength values, the energy barrier for oxygen escape from sinks and cross-section of oxygen-vacancy formation under gamma-irradiation have been estimated.

3. D.V. Kulikov, R.A. Suris, Yu.V. Trushuin, V.S. Kharlamov, D.N. Tsigankov. Computer simulation of the annealing of point magnetic-flux pinning centers in a neutron-irradiated YBaCuO single crystal. Tech.Phys.Lett. 22(11), 1996, p. 920-922.
   
   A model is presented for the evolution of point defects generated by neutron irradiation in YBaCuO. The concentrations of point defects generated by the neutron irradiaion are calculated. It is shown that by annealing the irradiated sample at room temperature (in the reactor channel) it is possible to form small clusters of point defects in concentrations sufficient for effective pinning of the magnetic flux. This model can explain the anisotropy in the lowering of the critical current density by annealing of irradiated samles and shows that the critical current in the presence of a magnetic field parallel to ab-plane is proportional to the concentration of pinning defects

4. F.M. Sauerzopf, M. Werner, H.W. Weber, R.A. Suris, D.V. Kulikov, V.S. Kharlamov, Yu.V. Trushin, Small Defects in YBCO Single Crystals: Tc After Neutron Irradiation and Annealing, Physica C, 282-289, p.1333-1334, (1997)
   
   Neutron irradiation of HTCs creates a wide spectrum of defect sizes. In this work, the influence of small defects on the critical temperature is investigated by sequential reactor neutron irradiation and annealing of a YBCO single crystal. The characteristic behaviour of Tc under this treatment is satisfactorily explained by a theoretical model considering the creation, migration and annihilation of small defects in the oxygen sublattice

5. Kulikov D.V., Suris R.A., Trushin Yu.V., Kharlamov V.S., Tsigankov D.N., Physical model of pinning centers annealing processes in neutron irradiated YBaCuO, Proc. of SPIE - The International Society for Optical Engeneering, v.3345, Jan.1998, pp.241 - 248
   
   Neutron irradiation of HTSCs creates a wide spectrum of defect sizes. In this work, the influence of small defects on the critical temperature and critical current density Jc is investigated. The characteristic behaviour of Tc and Jc under this treatment is satisfactorily explained by a theoretical model considering the creation, migration and annihilation of small defects in the oxygen sublattice.

6. D.V. Kulikov, Yu.V. Trushin, F.M. Sauerzopf, M. Zehetmayer, H.W. Weber Changes in the transition temperature after irradiation and annealing in single crystalline YBaCuO, submitted to Physica C
   
   We present a model of the defect dynamics in YBaCuO crystals to understand the changes in thr transition temperature after neutron irradiation and subsequent annealing. These changes are closely related to the calculated concentration of vacancies in the Cu-O chain sites.