vfrpkydrk rfkk fueurkfidh

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2 Z Z vfrpkydrk rfkk fueurkfidh izhkkx dk Qksdl ¼dsUnz fcunq½ izfrlfkk;h mpp rki vfrpkyd vksj vu; lac) inkfkks a dk ewy n`f"vdks.k jgk gsa iksyhfølvsykbu uewuks dh fofhkuu Jsf.k;ks a ds fo qr] pa qcdh;] FkeZy vksj volajpukred rduhdks a }kjk la'ysf"kr vksj vfhkyk{kf.kd (Characterized) fd;k x;k FkkA mues a ls dqn fueu gs tsls %& 0, 2, 4 vksj 6% lfgr Bulk MgB 2 uewus ftles a usuks&co 3 dks tksm+k x;k gs] dks la'ysf"kr fd;k x;k Fkk ftlls fd usuks&mksfiax }kjk foospukred djav l?kurk dh o`f) dk v/;;u fd;k tk lds A Mo (doped) Ruthenocuprates Ru 1-x Mo x (for x = 0.0, 0.2, 0.4, 0.6, 0.8 vksj 1.0) es a pq acdro vksj vfrpkydrk ds lg vflrro dh [kkst dh x;h FkhA Mn-izfrLFkk;h REBa 2 (RE=Y,Gd); 0<x<2%) vksj Y 0.95 Pr 0.05 Ba 2 (o < x < 2%) ds FkeZy O;ogkj (Behaviour) dh rqyuk dh x;h FkhA Pr 1-x vksj Sb-doped ¼lkekU;r% Mn Sites rd½ Pr 2/3 isjkosldkbv esxukbv~l ds lw{e volajpukred vkdkj lfgr fo qr vksj pqacdh; xq.k /keks a ds lecu/k dh [kkst dh x;h Fkh A

3 SUPERCONDUCTIVITY AND CRYOGENICS The focus of the division has been on the basic aspects of substituted high temperature superconductors and other related materials. Various series of polycrystalline samples were synthesized and characterized by electrical, magnetic, thermal and structural techniques. Some of them are as follows. Bulk MgB 2 samples with 0, 2, 4 and 6% added nano-co 3 were synthesized to study enhancement of critical current densities by nano-doping. Coexistence of magnetism and superconductivity in Mo doped ruthenocuprates Ru Mo Sr Eu Ce Cu O 1- (for x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) was investigated. Thermal behaviour of x x δ Mn-substituted REBa 2 (RE=Y,Gd); 0<x<2%) and Y 0.95 Pr 0.05 Ba 2 (0 x 2%) was compared. Relation of electrical and magnetic properties with micro-structural features of the Pr 1-x and Sb-doped (nominally at Mn sites) Pr 2/3 perovskite manganites were investigated.

4 vfrpkydrk rfkk fueurkfidh SUPERCONDUCTIVITY STUDIES Fluxiod jumps coupled high critical current density of nano-co 3 doped MgB 2 Polycrystalline MgB 2 samples with 0, 2, 4 and 6% added nano-co 3 being synthesized by vacuum (10-5 Torr) annealing at C for two and half hours each are found to be nearly single phase with presence of only a small quantity of Mg/ MgO in pristine sample and in addition the Co 2 O 3 in doped compounds. All the samples exhibited clear and sharp diamagnetic transitions at around 38 K, in Zero-field-cooled (ZFC) magnetic susceptibility measurements with sizeable signal. The Field cooled (FC) measurements though having sharp transitions, but showed a very small signal, indicating high level of pinning centers in these samples. Further some of the doped samples exhibited Paramagnetic-Meissner- Effect (PME) in applied field of 5 Oe. The critical current density (J c ), being estimated by invoking Bean s model for the pristine compound increase by nearly an order of magnitude for 2% and 4% nano-co 3 doping and later the same decreases sharply for 6% sample at nearly all studied temperatures and applied fields. Further the increased J c (~ 10 8 A/cm 2 ) is coupled with fluxoid jumps (T = 20 K and H = 1 T). Fluxoid jumps are not seen in relatively low J c pristine or 6% sample (Fig. 7.1). This means the fluxoid-jumps are intrinsic only to the high J c samples. Fig. 7.1 J c versus H plots for various n-co 3 doped MgB 2 samples. Fig.7.2 Transition temperature versus x plot for the Ru 1-x Mo x O 10 system Experimental study of magneto-superconductor Ru : Effect of Mo doping on magnetic behaviour and Tc variation" Mo doped ruthenocuprates Ru 1-x Mo x are synthesized for x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0, and their magnetic and superconducting properties are studied. It has been found that the magnetic transition temperature T ZFC peak, which corresponds to the appearance of weak ferromagnetic effect, decreases from its value of 75 K for x = 0.0 to 22 K, 25 K and 18 K, respectively for the x = 0.2, 0.4 and 0.6 samples. Another finding is that the magnetic susceptibility reduces at T ZFC peak by a factor of about 6, 85 and 413 for x = 0.2, 0.4, and 0.6 respectively. The samples of x = 0.8 and 1.0 are found to have no magnetic or superconducting effects. The values of the superconducting transition temperature are obtained from the resistivity versus temperature data. An important result is that Tc increases by 4.5 K and 7.0 K for x = 0.2 and 0.4 respectively, and then decreases by 17 K for x = 0.6. The observed variation of T c with x has been explained in terms of a theory which combines the effects of weakening magnetic behavior and reducing carrier concentration in a phenomenological manner (Fig. 7.2). The resulting theory is found to provide a good agreement with the observed value of T c. 74 okf"kzd izfrosnu 2005&2006

5 Superconductivity and Cryogenics data obtained are analyzed by using a narrow band model for the thermoelectric power and a phonon model for the thermal conductivity. It has been found that while the specific heat shows a jump at the superconducting transition temperature T c for x only, the thermal conductivity supports the presence of a superconducting energy gap at zero temperature for all values of x. Comparison of the parameters obtained from the analysis of the thermoelectric power and resistivity indicates a crossover of the role of Mn at x = Based on the thermoelectric power and thermal conductivity Fig.7.3 Magnetic susceptibility versus T plots for Bi 1.6 Pb 0.4 Cu 3-x Zn x O 10 system. Impact of Zn substitution on phase formation and superconductivity of Bi 1.6 Pb 0.4 Cu 3-x Zn x with x = 0.0, 0.03, 0.06, 0.09 and 0.12" Samples of series Bi 1.6 Pb 0.4 Cu 3-x Zn x with x = 0.0, 0.015, 0.03, 0.06, 0.09 and 0.12 are synthesized by solid-state reaction route. All the samples crystallize in tetragonal structure with majority (>90%) of Bi-2223 (Bi 2 Cu 3 O 10 ) phase (c-lattice parameter ~36 Å). The proportion of Bi-2223 phase decreases slightly with an increase in x. The lattice parameters a and c of main phase (Bi-2223) do not change significantly with increasing x. Superconducting critical transition temperature (T c ) decreases with x as evidenced by both resistivity [ρ (T)] and AC magnetic susceptibility [χ(t), Fig.7.3] measurements. Interestingly the decrement of T c is not monotonic and the same saturates at around 96 K for x >0.06. In fact Tc decreases fast (~10K/at%) for x = and 0.03 samples and later nearly saturates for higher x values. Present results of Zn doping in Bi-2223 system are compared with Zn doped other HTSC (High temperature superconducting) systems, namely the RE-123 (REBa 2 Cu 3 O 7 ) and La-214. Electrical and Thermal Investigations on RBa 2 O 7-ä (R=Gd,Y) Thermal behaviour (Specific heat, thermoelectric power and thermal conductivity) of superconducting samples GdBa 2 O 7-ä (x 0.02) has been investigated. Experimental results of the GdBa 2 O 7-ä and YBa 2 (Cu Mn ) O 1- systems with x = 0.0 and 0.005, it is x x 3 7-ä suggested that Gd +3 ions also affect the considered thermal behavior. Thermal conductivity (k) and thermoelectric power (S) on the Mn-substituted YBa 2 (0<x<2%) using a DC pulse technique and specific heat on Y 0.95 Pr 0.05 Ba 2 (0 x 2%) by semi-adiabatic heat pulse technique were investigated. Results indicate the normal state S(T) shows a concave behaviour for pure and low dopant concentrations; however, a convex behaviour is observed for samples with Mn concentrations of 1% and above. Significantly, replacing 1% Cu by Mn has little effect on the transition temperature; however, the change in S(T) is about a factor of eight. Specific heat jump of 3.8J/mol K, was observed only for pure Y-123 sample. However, no jump was observed in the doped samples. Detailed specific heat measurements carried out on pure and Mn-doped YBaCuO and GdBaCuO systems show that T c remains practically unchanged for YBaCuMnO with respect to Mn substitution but in contrast, a noticeable reduction in T c is observed in the GdBaCuO case. Prestine systems exhibit a clear jump in the specific heat at T c. However, a small Mn substitution caused a strong suppression in C p jump, suggesting that Mn is being incorporated into REBaCuO sytem as a whole and not in the form of a local cluster. Magneto-transport and morphological studies of Pr 1-x and Sb-doped Pr 2/3 Perovskites Electrical, magnetic and micro-structural features Annual Report

6 vfrpkydrk rfkk fueurkfidh of the Pr 1-x and Sb-doped (nominally at Mn sites) Pr 2/3 perovskite manganites were also investigated. Pristine material shows two insulator-metal (I-M) like transitions in the resistivity-temperature behavior. While the higher temperature transition (T P1 ) at ~195K is reminiscent of the usual metal-insulator transition, the lower temperature transition (T P2 ) at ~160K has been ascribed to the grain boundary (GB) effects arising out of the ionic size mismatch between the ions present at the rareearth site (Pr and Ba). LFMR results (at 0.15T) also substantiate the observed data. MR peaks near T P1 and increases further at lower temperatures, reflecting the grain boundary contribution. Susceptibility measurements show Curie transition (T c ) to be close to T P1 of the ñ-t data. Results are found to be consistent with other systems like (NdBa). Resistivity data on Pr 0.67 Sr 0.33 system, where the transition at T P2 is not seen due to smaller ionic size difference of (Pr +3 - Sr +2 ) than (Pr +3 - Ba +2 ), also corroborate these results. The resistivity upturn observed at low temperatures is considered in terms of the ensuing localization of carriers due to varying degree of ionic size mismatch in these systems. With Sb doping at the Mn-site, both the resistivity peaks are seen to shift to lower temperatures. Room temperature resistivity and the peak values are also successively increasing with Sb doping. Scanning micrographs of the samples indicate a gradual increase in their grain sizes with Sb which indicates a gradual decrease in the GB density. The higher temperature insulator-metal transition (T P1 ) shift is explained on the basis of a competition between double-exchange and superexchange mechanisms. The observed overall resistivity increase and the shift in the resistivity hump (T P2 ) with Sb are found related to the gradually decreasing GB density and the ensuing lattice strain increase at the grain boundaries. The intrinsic MR gets suppressed and extrinsic MR gets enhanced with Sb doping. The observed low temperature resistivity upturn related to the localization of carriers, is also seen to increase with Sb. Dielectric, Electrical and Microstructural Studies of W-doped SrBi 2 Ta 2 O 9 ferroelectric Ceramics Crystal structure, surface morphology, dielectric and electrical properties of tungsten doped SrBi 2 (W x Ta 1-x ) 2 O 9 (0.0 x 0.2) ferroelectric ceramics were investigated. Dielectric measurements performed as a function of temperature at 1 khz, 10 khz and 100 khz show an increase in Curie temperature (T c ) over the composition range of x=0.05 to W 6+ substitution in perovskite-like units results in a sharp dielectric transition at the ferroelectric Curie temperature with the dielectric constant at their respective Curie temperature increasing with tungsten doping. The dielectric loss reduces significantly with tungsten addition. The temperature dependence of ac and dc conductivity vis-à-vis tungsten content shows a decrease in conductivity that is attributed to the suppression of oxygen vacancies. The activation energy calculated from the Arrhenius plots is found to increase with tungsten content. 76 okf"kzd izfrosnu 2005&2006