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Bond Valence Sum (BVS) calculations were performed on neutron diffraction (ND) data measured at 12, 35, 55, 75 and 300 K on one sample (x = 0.3), of a series of La2-xDyxCa2xBa2Cu4+2xOz (La-2125) compounds. ND experiments have been carried out to study the effect of temperature on structure and to relate it with the superconducting properties. The sample, La1.7Dy0.3Ca0.6Ba2Cu4.6Oz (LD3) has been reported earlier, and exhibits superconductivity at 68 K. In this paper we discuss BVS calculations carried out on low temperature neutron diffraction data.

The La-2125 type La2-xDyxCa2xBa2Cu4+2xOz (0.1 < x < 0.5; LDBO) compounds have been synthesized and studied for their structural and superconducting properties by room temperature neutron diffraction, high field dc magnetization, four-probe resistivity and iodometric double titration. The Rietveld analysis of the neutron diffraction data reveals tetragonal structure for all the samples, which crystallizes into La-123 type tetragonal structure in P4/mmm space group. Iodometric double titrations were performed to determine the oxygen content values and calculate mobile charge carrier (holes) density. The superconducting transition temperatures (Tc) increases from ~ 20 K for x = 0.1 to a maximum of 75 K for x = 0.5. Flux pinning force (Fp) and critical current density (Jc), calculated from the low temperature hysteresis loops, also increases with increasing dopant concentration. The paper presents the studies on structure and superconducting properties of all LDBO compounds in light of the role of calcium in inducing superconductivity in the tetragonal non-superconducting oxide., To appear in J. Phys. Condens. Matter

Polycrystalline La2-xPrxCa2xBa2Cu4+2xOz (LPCaBCO) compounds with x = 0.1 - 0.5 were synthesized by solid-state reaction method and studied by room temperature X-ray diffraction, dc resistivity, dc magnetization and iodometry. The superconducting transition temperatures in these tetragonal triple perovskite compounds increases from 32 to 62 K (Tconset values) with increasing dopant concentration. The mixing of rare earth La3+ and Pr3+/4+ ions at rare earth site (La3+) along with substitution of divalent Ca2+ results in the shrinkage of unit cell volume. The contraction of unit cell volume due to larger ion being substituted by smaller ions, gives rise to creation of pinning centers in the unit cell leading to increase in critical current density and flux pinning, To be published in Solid State Communications (2004)

We present here our studies on Zn-doped La 1.5 Nd 0.5 Ca 1 Ba 2 Cu 5 O z (La-2125), tetragonal superconductor. Eight different compositions of La 1.5 Nd 0.5 Ca 1 Ba 2 (Cu 1− x Zn x ) 5 O z ( x =0.00–0.04), were studied through X-ray diffraction, SEM, a.c. susceptibility, resistivity, magnetization measurements and iodometric analysis to explore effects of Zn doping on the structural and superconducting properties. The Rietveld analysis of XRD data shows that all the samples form in tetragonal structure (space group P4/mmm ). A.c. susceptibility and resistivity measurements showed that, superconducting transition temperature, T c , is suppressed with increasing Zn in the system at the rate of ∼6–7 K per atomic percent of Zn. The superconducting transition of these materials is found to be highly dependent on dopant concentration. The critical current density J c ( H ), determined from magnetization measurements, is found to be ∼10 5 –10 6 A/cm 2 at low fields. For x =0.01 and 0.015, J c is higher at all fields and is nearly double than that of the pristine La-2125. The enhancement in J c ( H ) is ascribed to the effective flux line pinning by nonmagnetic Zn at Cu–O planes in this system. For higher concentrations, due to competition between increase of J c arising from pinning by Zn and decrease of J c arising from pair breaking effect of Zn, a cross over is seen in the J c ( H ) of doped and pristine samples.

The La2-xPrxCayBa2Cu4+yOz (LaPrCaBCO) mixed oxides have been studied for their structural and superconducting properties using X-ray diffraction (XRD), d. c. resistivity, d. c. susceptibility and iodometric double titration. All the LaPrCaBCO samples for x = 0.1 - 0.5, exhibit tetragonal crystalline structure with P 4/mmm space group as determined by Rietveld analysis of the X-ray diffraction data. With increasing x, enhancement in Tc is observed, which is quite interesting for Pr substituted high Tc oxides. Maximum Tc ~ 58 K has been observed for x = 0.5(La-2125 stoichiometry). The results of structural studies and superconducting property measurements are presented in light of increase in Tc in LaPrCaBCO system with increasing Pr concentration.

Mo-substituted triple perovskite superconducting samples with the stoichiometric composition La(1.5)Nd(0.5)Ca(1)Ba(2)[Cu(1-x)Mo(x)](5)O(z), [LNCBCuMO] with x = 0.00, 0.01, 0.03, 0.05 and 0.10, have been investigated using X-ray diffraction, electrical resistivity, magnetic susceptibility, magnetization and oxygen content measurements. The observed reduction in Tc with increasing Mo content (x) in LNCBCuMO, can be attributed to the decrease in hole concentration. Magnetization measurements as a function of temperature and field (H), exhibit an M-H hysteresis loop, which indicates moderate flux pinning, which can be attributed to the pinning centers created by Mo substitution at Cu sites. The critical current density, Jc, deduced from the M-H data satisfies the flux creep model.

A new series of mixed oxide superconductors with the stoichiometric composition La2−xDyxCayBa2Cu4+yOz (x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La2−x(Y/Er)xCayBa2Cu4+yOz series, show a strong dependence of Tc on hole concentration (psh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant displacement of La onto Ba site. Superconductivity studies show that maximum Tc is obtained for x=0.5, y=1.0 sample (Tc ∼ 75 K), for La1.5Dy0.5Ca1Ba2Cu5Oz (La-2125).

Crystallographic studies on the (La2 − xNdx)CayBa2Cu4 + yOz′ [y = 2x; 0.0 ≤ x ≤ 0.5] samples are carried out using neutron diffraction technique. The analysis of the neutron diffraction patterns for the series of samples with 0.0 ≤ x ≤ 0.5 was done using Rietveld method. The La2Ba2Cu4Oz′ (La-224, x = 0.0) system exhibits tetragonal phase and is a nonsuperconductor, which on addition of a “CaCuO2” rock salt like layer becomes superconducting. It is important to note the significant role played by Ca-doping in improvising the superconducting properties. Analysis of the structural data reveals that, as Ca concentration increases, the unit cell volume decreases while Tc increases with a maximum value of 78 K for y = 1.0. The detailed crystal structure for LaNdCaBCO series of samples has been studied in the light of changes in bond lengths with increase in Ca concentration and its role in “turning on” the superconductivity.

We report the effect of Sr-substitution in restoring the superconductivity of Pr-doped (Eu 1− x Pr x )Ba 2 Cu 3 O z [A] and Eu(Ba 2− x Pr x )Cu 3 O z [B] samples. The structural and superconducting properties of these A and B samples have been investigated using X-ray diffraction, a.c. susceptibility, electrical resistivity, d.c. magnetization and iodometric measurements. It is observed that the superconductivity gets suppressed at the rate of 1.6 K per at.% of Pr substitution at Eu-site due to the localization of mobile holes, while the sample with 15% Pr at Ba-site [B(0.3)] becomes non-superconducting mainly due to the hole filling and localization of holes. However, the increasing substitution of Sr at Ba-site in both A(0.4) and B(0.3) samples upto 25% resulted in the restoration of superconductivity (T c ∼33 K ) due to the delocalization of holes. Interestingly, the increasing substitution of Sr at Eu-site in the non-superconducting B(0.4) sample upto 30%, increases T c from 0 to 52 K mainly due to the hole doping mechanism which is much faster and larger restoration of superconductivity than the Ba-site doping of Sr in the same sample.

The structural and superconducting properties of Cu–Co and coupled Gd–Ca/Cu–Co substitution in GdBa 2 Cu 3 O 7− δ have been studied by X-ray diffraction for crystal structure determination, resistivity, a.c. susceptibility for T c determination and iodometry for oxygen content measurements. The oxides (Gd 1− y Ca y )Ba 2 (Cu 1− x Co x ) 3 O 7− δ have been synthesised for 0.0≤ x ≤0.15 and 0.0≤ y ≤0.45. The effect of increasing Co-concentration in GdBa 2 (Cu 1− x Co x ) 3 O 7− δ for 0.0≤ x ≤0.15 is to lower the carrier concentration and decrease T c which is attributed to the hole filling by Co. This suppression in T c has been compensated for by appropriate hole doping with Ca, in (Gd 1− y Ca y )Ba 2 (Cu 1− x Co x ) 3 O 7− δ which shows that for a fixed Co-content T c increases dramatically as the Ca-content increases leading for instance to the oxides x =0.1, y =0.3; x =0.12, y =0.36 and x =0.15, y =0.45 with respective T c ’s of 83 K, 68 K and 63 K whereas the nonsubstituted phases x =0.1, 0.12, 0.15, y =0.0 don’t superconduct.

The structural and superconducting properties of single-phase Fe-substituted La 2.5 Nd 0.5 CaBa 3 (Cu 1− x Fe x ) 7 O z (LNCBCuFe) with 0.0⩽ x ⩽0.06 compounds having triple-perovskite structure are investigated using X-ray diffraction, a.c. susceptibility, d.c. magnetization, oxygen content and Mossbauer effect measurements. Mossbauer spectral analysis of x =0.03 sample displays unusual Fe-dopant site occupancies and the Cu(2) plane to Cu(1) chain site ratio in the LNCBCuFe are quite different from those of the usual Fe-doped YBa 2 Cu 3 O 7− δ . Specifically, we observe substantial occupation of a new chain-associated quasi-octahedral site, E, at 300 K which transforms into the well-known distorted tetrahedron chain site, A, on lowering the temperature to 78 K. The observed reduction of T c with increasing x in LNCBCuFe supports the view that the hole filling mechanism contributes predominantly to the suppression of superconductivity by Fe.

It has been reported that, by adding equal amounts of CaO and CuO to non superconducting La3Ba3Cu6O z (La-336), a series of superconductors with nominal compositions La3Ca y Ba3Cu6+yO z were prepared with maximum Tonc ∼ 80K. Similar studies on addition of CaO and CuO in nonsuperconducting LaBaCu2O z (La-112) resulted into superconducting LaCaBaCu3O z (La-1113). To date no attempt has been made to synthesize La2CaBa2Cu5O z (La-2125) superconducting phase by addition of CaO and CuO to non superconducting La2Ba2Cu4O z (La-224) system. Also no reports are published to study the effect of replacing larger La3+-ions (1.01A) by smaller rare earth ions viz Y3+(0.89A), Er3+(0.91A), Gd3+(0.91A) on the structural and superconducting properties of (La2−xR x )Ba2(Ca y Cu4+y)O z (LRBCaC); 0.0 ≤ x ≤ 0.5; y=2x system. In this paper, we report the method of synthesis, structural and superconducting property characterization using X-ray diffraction, oxygen content measurements using iodometry, resistivity measurements using d.c. four probe technique and a.c. susceptibility measurements in the temperature range RT to 15K. Also a comparative study, on the evolution of superconducting phase with Ca-concentration for different rare earth substitutions for LRBCaC system in the context of hole doping mechanism, is carried out.

The structural and superconducting properties of Nd- and Ca-substituted (Nd1-xCax)(Ba2-yNdy)Cu3Oz samples prepared under identical conditions have been investigated by x-ray diffraction, resistivity, ac susceptibility and oxygen content measurements. The effect of increasing Nd concentration in NdBa2-yNdyCu3Oz lowers the carrier concentration and decreases Tc, which is attributed to magnetic pair breaking by local moments and hole filling by Nd. This suppression in Tc has been compensated by appropriate hole doping with Ca in (Nd1-xCax)(Ba2-yNdy)Cu3Oz, which shows that for a fixed Nd content at the Ba site Tc increases dramatically as the Ca content increases. For instance, in the oxide (Nd1-xCax)(Baz-yNdy)Cu3Oz, the Tc increases from 0.0 K (x = 0.0, non-superconductor) to 77.5 K (x = 0.4, compensated oxide) as the magnetic pair breaking and hole filling by Nd is nearly balanced by hole doping from Ca.

The structural and superconducting properties of La- and Ca-substituted (Nd1−xCax)(Ba2−yLay)Cu3Oz samples prepared under identical conditions have been investigated by X-ray diffraction (XRD), resistivity, ac susceptibility and oxygen content measurements. The effect of increasing La-concentration in Nd(Ba2−yLay)Cu3Oz is in lowering the carrier concentration and decreasing Tc, which is attributed to hole-filling by La. This suppression of Tc has been compensated by appropriate hole-doping with Ca in (Nd1−xCax)(Ba2−yLay)Cu3Oz, which shows that for a fixed La content at Ba-site, Tc increases dramatically as the Ca content increases. For instance, in the oxide (Nd1−xCax)(Ba1.6La0.4)Cu3Oz, the Tc increases from 0.0 K (x=0.0, non-superconductor) to 84.0 K (x=0.4, compensated oxide) as the hole-filling by La is completely balanced by hole-doping from Ca.

The structural and superconducting properties of single-phase Fe-substituted La 2.5 Y 0.5 CaBa 3 (Cu 1− x Fe x ) 7 O z [LYCBCuFe] with 0≤ x ≤0.15 compounds having triple-perovskite structure are investigated using X-ray diffraction, resistivity, AC Susceptibility, oxygen content and Mossbauer effect measurements. The observed reduction of T c with increasing x in LYCBCuFe supports the view that magnetic pair breaking by local moments contributes predominantly to the suppression of superconductivity by Fe. The observed Fe-dopant site occupancies and the Cu(2) plane to the Cu(1) chain site ratio in the LYCBCuFe obtained from Mossbauer spectral analysis of x =0.02 sample are quite different from those of the usual Fe-doped YBa 2 Cu 3 O z .

The superconducting properties of single phase La1·5−x Ca x+y Ba1·5−y Cu3O z , 0·0≤x≤0·60 (LC) and 0·0≤y≤0·70 (CB), compounds with tetragonal triple-perovskite structure are studied, using X-ray diffraction for their resistivity, a.c. susceptibility, and oxygen-content. La1·5−x Ca x Ba1·5Cu3O z (LC) samples, 0·15≤x≤0·60, are superconducting withT c =0 between 40 and 74 K. With the increase inx, the oxygen content, hole concentration in the CuO2 layers as well as theT c increase. It is interesting to find that although the hole concentration and oxygen stoichiometry of the LaCa0·5+y Ba1·5−y Cu3O z (CB) compounds increase with the increase iny, theT c =0 remains nearly constant around 74 K fory=0·0−0·70. A correlation exists between theT c and the hole concentration for LC and CB compounds.

The structural and superconducting properties of (Gd1−yCay)Ba2(Cu1−xMox)3Oz samples are investigated using X-ray diffraction, A.C. susceptibility, electrical resistivity and oxygen content measurements. The effect of increasing the Mo concentration in GdBa2(Cu1−xMox)3Oz changes the structure from orthorhombic to tetragonal, accompanied by an increase in the normal state resistivity and decreases both the oxygen content and Tc, which is attributed to hole filling by Mo. This suppression in Tc has been compensated for by appropriate hole doping with Ca, for instance in the oxide (Gd1−yCay)Ba2(Cu0.92Mo0.08)3Oz, the Tc increases from 27 K (y=0.0) to 86.5 K (y=0.24, compensated oxide), closer to the value of 91 K for pure GdBa2Cu3O7−δ due to the balance between the hole filling by Mo and hole doping by Ca.

The structural and superconducting properties of (Gd1−x−yCa y M x )Ba2Cu3O z with M = Mo, Hf are investigated using X-ray diffraction, electrical resistivity, and oxygen content measurements. The effect of increasing the Mo concentration in (Gd1−xMo x )Ba2Cu3O z changes the structure from orthorhombic to tetragonal accompanied by a large increase in resistivity and a fast decrease in Tc at the rate of 1.9 K per at.% of Mo, unlike that of Hf substitution in (Gd1−xHf x )Ba2Cu3O z , which maintains the orthorhombic structure and decreases Tc very slowly at the rate of 0.6 K per atm.% of Hf with nearly no change in resistivity. The suppression of Tc by M = Mo, Hf can be counterbalanced by hole doping by Ca which increases Tc with increasing Ca content showing maximum compensation for Mo. A comparative study of M = Mo, Hf doped samples in (Gd1−x−yCa y M x )Ba2Cu3O z indicates that the valence of the dopant M = Mo4+,6+, Hf4+ and its ionic radius play an important role in controlling the structural and superconducting properties of the systems.

The structural and superconducting properties of single-phase La2.5−y Y0.5Ca1+y Ba3 (Cu0.88Fe0.12)7O z (LYCaBCuFe) (y= 0.0−1.0) compounds with triple perovskite structure are investigated using X-ray diffraction, resistivity, a.c. susceptibility, and oxygen content measurements. Increasing Ca substitution for La resulted in a decrease in unit cell axes and volume. T c R=0 shows a marginal increase from 31 K to 37 K for y = 0.0−0.21 and thereafter it decreases with increasing y leading to zero T c R=0 at y ≥ 0.84. This shows that the suppression of T c from 80 K to 31 K by Fe doping at x = 0.12 La2.5Y0.5CaBa3(Cu1−x Fe x )7O z cannot be compensated by appropriate hole doping with Ca in LaYCaBCuFe.

We report the results of temperature dependent magnetotransport measurements on PLD grown GdBa2Cu3OZ (Gd-123) film in the superconducting transition region, TC0 < T < TConset. It is observed that, on application of magnetic field (0 – 14T), TConset (temperature at which superconducting transition starts) remains unchanged while TC0 (temperature at which resistance becomes zero) gets suppressed with field, resulting in the increase in superconducting transition width (ΔTC). Effect of applied field on the flux dynamics, in superconducting transition region, has been understood in the light of thermally activated flux flow (TAFF) model and variation in pinning energy (U0) in Gd-123.

The structural and superconducting properties of ( samples have been studied by x-ray diffraction, resistivity, a.c. susceptibility and oxygen content measurements. The effect of increasing La concentration in is in lowering the carrier concentration and decreasing , which is attributed to hole filling by La. This suppression of has been compensated by appropriate hole doping with Ca in (, which shows that for a fixed La content increases dramatically as the Ca content increases. For instance, in the oxide (, the increases from 35 K (x = 0.0) to 82 K (x = 0.4, compensated oxide) as the hole filling by La is completely balanced by hole doping form Ca.

The structural and superconducting properties of (Gd 1− x − y Ca y Mo x )Ba 2 Cu 3 O z samples are investigated using X-ray diffraction, ac susceptibility, electrical resistivity and oxygen content measurements. The effect of increasing the Mo concentration in (Gd 1− x Mo x )Ba 2 Cu 3 O z changes the structure from orthorhombic to tetragonal accompanied by an increase in the normal state resistivity and decreases both the oxygen content and T c which is attributed to hole filling by Mo. The substitution of Ca for Gd in (Gd 0.85− y Ca y Mo 0.15 )Ba 2 Cu 3 O z provides proper matching between the ionic radius and valence of Gd 3+ (0.94 A) and the average ionic radius and valence of Mo 4+ (0.70 A) and Ca 2+ (0.99 A). As the Ca content increases, the T c increases from 58.5 K ( y = 0) to 86 K ( y = 0.15, compensated oxide), closer to the value of 91 K for pure GdBa 2 Cu 3 O 7−δ due to the balance between the hole filling by Mo and hole doping by Ca.

The structural and superconducting properties of Y1−v−ηPrNCd{η}¨zCazBa2Cu3O7−δsystem are investigated using X-ray diffraction, ac susceptibility, dc resistivity, and oxygen content measurements. The effect of increasing Cd concentration substituting the Y-site in Y0.8Pr0.2Ba2Cu3O7-δ suppresses the superconducting transition temperature and lowers the hole concentration, unlike that of Ca substitution in Y0.8Pr0.2Ba2Cu3O7-δ which increasesTc due to hole doping by Ca. The suppression ofTc due to Cd substitution can be counterbalanced by simultaneous hole doping by Ca which increases the Tc with increasing Ca concentration. In spite of similarity in the ionic radii and valency, the role played by Cd and Ca substitution at the Y-site in the Y0.8Pr0.2Ba2Cu3O7-δ system is opposite in nature as Cd doping helps in Tc suppression due to the Pr effect, suggesting that Cd does not provide the necessary holes like Ca substitution which helps to increase the Tc by the hole doping mechanism.

The structural and superconducting properties of single phase La 3.5− x – y R y Ca 2 x Ba 3.5− x Cu 7 O z (0 ≤ x = y ≤ 0.70) (LRCB with R = Gd, Nd and Dy compounds with tetragonal triple-perovskite structure are investigated using X-ray diffraction, resistivity, AC susceptibility and oxygen-content measurements. Increasing Ca and Gd substitution for La and Ca for Ba resulted in a decrease in unit cell axes and an increase in oxygen stoichiometry. Samples with 0.2 ≤ x = y ≤ 0.70 are superconducting and T c R = 0 is between 31 and 79 K. With increasing x = y , both the hole concentration in the Cu2-O layers and T c R = 0 increase to a maximum value of 0.313 and 79 K at x = y = 0.6, respectively. A correlation between the T c and the hole concentration is suggested. Similar superconducting behaviour has been observed for R = Nd and Dy in LRCB compounds.

The structural and superconducting properties of (Er1-xCax)Ba2-ySry(Cu2.76Co0.24)Oz are investigated using X-ray diffraction, resistivity, ac susceptibility, and oxygen content measurements. Increasing the Sr content in (Er0.76Ca0.24)Ba2-ySry(Cu2.76Co0.24)Oz lowers the oxygen content and decreases theT c, which is attributed to the rearrangement of oxygen atoms in the basal plane. This suppression ofT c aty =0.6 cannot be improved by appropriate hole doping with Ca in (Er1-xCax)Ba1.4Sr0.6(Cu2.76Co0.24)Oz forx = 0.24-0.48.

The structural and superconducting properties of CuCo and coupled ErCa CuCo substitution in ErBa2Cu3O7 − δ have been studied using X-ray diffraction, a.c. susceptibility, resistivity and oxygen content measurements. The oxides (Er1 − yCay)Ba2(Cu1 − xCox)3Oz have been synthesized for 0 ≤ x ≤ 0.15 and 0 ≤ y ≤ 0.45. The effect of increasing the Co-concentration in ErBa2(Cu1 − xCoxOz for 0 ≤ x ≤ 0.15 is to lower the carrier concentration and decrease Tc, which is attributed to the hole filling by Co. This suppression in Tc has been compensated for by appropriate hole doping with Ca, in (Er1 − yCay)Ba2(Cu1 − xCox)3Oz, which shows that for a fixed Co-content Tc increases dramatically as the Ca-content increases, leading, for instance, to the oxide (Er0.55Ca0.45)Ba2(Cu0.85Co0.15)3O6.81 (to a Tc of 71 K), whereas the non-substituted phase ErBa2(Cu0.85Co0.15)3O6.70 does not superconduct. As a result, the ‘compensated oxide’ (Er1 − yCay)Ba2(Cu − xCox)3Oz exhibits an almost x-independent Tc ranging from 86 to 84 K for 0.12 ≤ y = 3x ≤ 0.24.

The structural and superconducting properties of (Er1−yCay)Ba2 (Cu1−xCox)3Oz samples are investigated using X-ray diffraction, resistivity and oxygen content measurements. The effect of increasing Co concentration in ErBa2(Cu1−xCox)3Oz lowers the carrier concentration and decreases Tc, which is attributed to hole filling by Co. This suppression of Tc has been compensated by appropriate hole doping with Ca, for instance, in the oxide (Er1−yCay)Ba2(Cu0.94Co0.06)3Oz, the Tc increases from 34 K (y = 0.0) to 85 K (y = 0.18, compensated oxide) as the hole filling by Co is completely balanced by hole doping from Ca.

The structural and superconducting properties of (Er1−y−yCayHfx)Ba2Cu3Oz samples are investigated using X-ray diffraction, resistivity, AC susceptibility and oxygen-content measurements. The effect of increasing the Hf concentration in Er−xHfxBa2Cu3Oz lowers the oxygen content and decreases Tc which is attributed to hole filling by Hf. The substitution of Ca for Er in (Er0.85−yCayHf0.15)Ba2Cu3Oz provides a proper matching between the ionic radius and valence of Er3+ (0.88 A) and the average ionic radius and valence of Hf4+ (0.78 A) and Ca2+ (0.99 A). As the Ca content increases, the Tc increases from 70 K (y = 0.05) to 86 K (y = 0.25, compensated oxide), closer the value of 91 K for pure ErBa2Cu3O7−δ due to the balance between the hole filling by Hf and hole doping by Ca.

The effects of Sc and Ti substitutions on magnetic and superconducting properties of DyBa 2 (Cu 1− x M x ) 3 O 7− z , (M=Sc or Ti, x =0.00,0.03,0.05,0.10) system have been investigated. Decrease of T c with increasing Sc or Ti dopings in the system is observed, which is attributed to hole-filling mechanism. The paramagnetic moment (∼10.4 μ B / f.u .) from Curie–Weiss fit is found to be slightly less than the paramagnetic moment of free Dy 3+ ion. The observed dopant concentration dependent upward curvatures in magnetization in diamagnetic region are discussed in the light of various possibilities.

Pr substituted at constant Ca concentration for Y in (Y1−x−yPrxCay)Ba2Cu3O7−δ superconductors have been prepared under identical conditions and the temperature dependence of the electrical resistivity of these samples are measured. The resistively determined values of Tc decrease linearly with increasing x (0 ≤ x ≤ 0.2) for constant y = 0.10 and 0.15 which provides convincing evidence that the suppression of superconductivity by Pr is mainly due to magnetic pair breaking. The suppression of superconductivity can also be correlated to the observed changes in oxygen content determined by iodometric analysis and to the average Cu-valences. However, it is found that the observed suppression of Tc cannot be compensated by appropriate hole doping with Ca.

We provide a recipe to process oxygen-rich Fe-doped YBa2Cu3O7−δ samples, which display unusual Fe-dopant site occupancies and superconducting properties. Specifically, we observe substantial occupation of a chain-associated quasi-octahedral site (site E). Room-temperature aging of such samples at ambient conditions leads to the extinction of site E and a concomitant growth of other chain sites, and an increase in Tc. The aged samples display the usual Fe-dopant site distribution and Tc's reported by numerous groups for this superconductor.

Ca-substituted (Er 1− x Ca x )Ba 2 Cu 3 O y superconductors have been prepared under identical conditions and the temperature dependence of the electrical resistivity of samples are measured (0⩽ x ⩽0.3). The oxygen content of the samples ( x =0-0.3) were determined by the iodometric method. The interrelationship between the superconducting transition temperature T c and the variation of oxygen content has been discussed in terms of the Cu valence. The observed reduction of T c with increasing x in (Er 1− x Ca x )Ba 2 Cu 3 O y supports the view that magnetic pair breaking by local moments and hole doping contribute substantially to the suppression of the superconductivity by Ca.

Pr- and Ca-substituted (Er1-x-yPrxCay)Ba2Cu3O7- delta superconductors have been prepared under identical conditions and characterized according to resistivity and AC susceptibility measurements. The observed reduction of Tc with x in (Er1-xPrx)Ba2Cu3O6.90 for 0

A nonsuperconducting La2Ba2Cu4O9+δ system has been made superconducting by the addition of CaCuO2, along with rare earth doping at the La site, with the stoichiometric composition La2−xRxCayBa2Cu4+yO10+δ (R=Nd, Gd, and y=2x). All the samples with 0.0

The structural and superconducting properties of Ga substituted for Cu in NdBa 2 Cu 3 O 7− δ samples have been studied by X-ray diffraction, resistivity, AC susceptibility and oxygen content measurements. The effect of increasing Ga concentration in NdBa 2 (Cu 1− x Ga x ) 3 O z reduces orthorhombicity very fast displaying the destruction of oxygen vacancy order (OVO) for x ⩾0.03 accompanied by an increase in the normal state resistivity and decreases both carrier concentration and T c , which is attributed to hole filling by Ga. The calculated hole concentration from oxygen content data and T c display a strong correlation between the two.

Pr- and Ca-substituted (Y 1− x − y Pr x Ca y )Ba 2 Cu 3 O 7−δ superconductors have been prepared under indentical conditions and characterized according to resistivity, AC susceptibility and DC magnetization measurements. The observed reduction of T c with increasing x in (Y 1− x Pr x )Ba 2 Cu 3 O 7−δ supports the view that magnetic pair breaking by local moments and hole localization/ filling contribute substantially to the suppression of superconductivity by Pr and clearly demonstrates that this suppression can be compensated by appropriate hole doping with Ca. The observed variation in T c with increasing y in (Y 1− y Ca y )Ba 2 Cu 3 O 7−δ may be attributed to the dilution of magnetic interactions and hole doping by Ca. DC magnetization measurements on randomly oriented powdered systems exhibit pronounced M ( H ) hysteresis loops, indicative of extensive flux pinning even as T approaches T c . We feel that this flux pinning arises due to the Pr or PrCa acting as pinning centres. The critical current density J c deduced from hysteresis data is found to be directly related to the mobile hole concentration.

Nickel (Ni) doped YBa 2 Cu 3 O 7−δ samples prepared under identical conditions have been characterized by resistivity, a.c. susceptibility and d.c. magnetization measurements. Detailed magnetization measurements on randomly orientated powdered samples as a function of temperature and field exhibit pronounced M ( H ) hysteresis loops indicative of large flux pinning, even as T approaches T c . It is believed that the flux pinning arises due to the preferential substitution of Ni on the Cu(2) site, which acts as a pinning centre. A critical current density, J c of |≈ 10 6 A cm −2 is deduced from M ( H ) data at 13 K in a 1.5 kOe field for YBa 2 (Cu 1- x Ni x ) 3 O 7−δ ( X = 0.01, 0.02 and 0.03) samples, which is nearly five times higher than the J c of the pristine 1-2-3 powdered sample.

Zn-substituted YBa2(Cu1-xZnx)3O7- delta superconductors have been synthesized, and characterized according to resistivity, AC susceptibility and DC magnetization measurements. DC magnetization measurements on randomly oriented powdered systems exhibit pronounced M(H) hysteresis loops, indicative of extensive flux pinning. The authors feel that this flux pinning arises due to the Zn acting as a pinning centre. The critical current density Jc has been deduced from hysteresis data.

We have deposited c-axis oriented thin films of La1.5Dy0.5CaBa2Cu5Oz (La-2125) tetragonal superconductor on LaAlO3 (001) by Pulsed Laser Deposition. These films were irradiated with 200 MeV Ag+15 ions. Atomic Force Microscopy and Elastic Recoil Detection Analysis indicate that the irradiation has created columnar defects along the entire thickness (2000 A) of these films. With ion irradiation up to 1*10^11 ions/cm2, the critical current density (Jc(H)) is found to enhance by almost five folds, which is attributed to the augmented flux pinning by the columnar defects. A further increase in irradiation to 1*10^12 ions/cm2 causes reduction in Jc(H) due to distorted morphology of the film. Our work shows that the enhancement in Jc (H) of the irradiated La-2125 film is comparable to that in irradiated RE-123. Also, as the La-2125 type films have greater chemical stability than RE-123 (RE = rare earth ion), La-2125 type superconductors are potential candidates for applications. Interesting to note that there are partial flux jumps observed to occur symmetrically in the magnetic hysteresis of irradiated La-2125 thin films with enhanced Jc(H)., Comment: 13 pages including 4 figures

Structural studies on Dy-substituted La-2125 type superconductors have been carried out by neutron diffraction experiments at room temperature using a monochromatic neutron beam of wavelength lambda = 1.249 Angstroms. A series of samples with La2-xDyxCa2xBa2Cu4+2xOz stoichiometric composition, for x = 0.1 - 0.5, have been studied for their structural properties. A tetragonal Y-123 unit cell was taken as the starting model for the Rietveld analysis. All the samples fit into the starting model, exhibiting no structural transition taking place with increasing dopant concentration. The results of Rietveld analysis and structural properties are discussed in detail.

The effect of Co-Ga paired substitution on the superconducting properties of YBa2Cu3O7-d (Y-123) has been investigated by X-ray diffraction, ac susceptibility,dc resistivity and oxygen content measurements. We report in this paper the results of our studies on the paired substitution of a magnetic and non-magnetic ion at Cu site in Y-123, while keeping the total dopant concentration fixed. The simultaneous substitution of Co and Ga at Cu site shows variation in the transition temperature (Tc), oxygen content and hole concentration as a function of change in the balance of magnetic (Co) and non-magnetic (Ga) concentration. Orthorhombicity (D), given as (b-a)/a, also varies as a function of increasing dopant concentration. The variation in Tc due to Co-Ga substitution is discussed in the light of dopant valency and hole filling mechanism., Comment: To appear in Mod. Phys. Let. B; PDF file only

The structural and superconducting properties of YBa2(CU1−x Ti x )3Oz samples are investigated using X-ray diffraction, ac susceptibility, and oxygen content measurements. The effect of increasing Ti concentration in YBa2(Cu1−x Ti x )3Oz lowers the oxygen content and decreasesT c, which is attributed to hole filling by Ti.

The authors report on the successful synthesis of single-phase Zr-substituted YBa{sub 2}(Cu{sub 1-x}Zr{sub x})O{sub 7-{delta}} superconductors up to 5 at.% (x = 0.0-0.05) and characterized them according to resistivity and ac susceptibility measurements. The authors did not observe any significant change in orthorhombicity and in {Tc} similar to Ni{sup 2+}- and Nb{sup 5+}-doped systems.

Co‐doped YBa2Cu3O7−s samples prepared under identical conditions have been investigated by magnetization measurements as a function of temperature and field exhibiting pronounced M(H) hysteresis loops indicative of large flux pinning even as T approaches Tc. It is believed that the flux pinning arises due to the preferential substitution of Co in Cu(1) site, which acts as pinning center. A critical current density, Jc, of ∼106 A/cm2 is deduced from M(H) data at 13 K in a field of 1.5 kOe for YBa2(Cu1−xCox)3O7−s at x=0.01, which is nearly five times larger than the Jc of the pristine 1‐2‐3. The variation of Jc with atomic percent of Co‐substitution in 1‐2‐3 shows a structural transition (orthorhombic to tetragonal) at 4 at. % of Co indicating structural dependence on Jc.

We report the synthesis and characterization of superconducting La2.5−x−y(Yb)xBa2.5−yCa2yCu5Oz (0.0

With a view to monitor the formal valence of copper in YBaCuO system, substitutions of divalent (Ca) and tetravalent (Pr) impurities at Y‐site have been carried out. In addition to this the cooperative effect of these substitutions at Y‐site on the structural and superconducting behavior of YBaCuO system has been investigated using X‐ray and susceptibility measurements. The changes in the superconducting transition temperature have been discussed in the context of oxygen content and changes in the formal copper valence in the YBaCuO system.

A systematic study of (Er1−xMx)Ba2Cu3O7−d with M=Hf4+, Pr3+→4+, Ca2+ has been caried out with an objective of investigating the effect of dopant valency and magnetic moment on hole filling, pair breaking and hole doping mechanisms in influencing the superconductivity. It is found that non magnetic Hf-substitution up to x=0.2 shows that the reduction in Tc is mainly due to hole filling, whereas the substitution of Pr (up to x=0.2) displays suppression of Tc due to both hole filling and pair breaking mechanisms, as Pr possesses fluctuating valence and magnetic moment. In the case of non magnetic Ca-substitution, the Tc decreases due to hole doping and pair breaking mechanisms. The comparative results on these three systems will be discussed in the light of pair breaking, hole doping and hole filling mechanisms through empirical relations.

The structural and superconducting properties of single phase (La2−xYx)Ba2(CayCu4+y)Oz (0.0≤x≤0.5, 0.0≤y≤1.0) compounds with tetragonal triple perovskite structure are investigated using X-ray diffraction, resistivity and oxygen content measurements. Samples with 0≤x≤0.5 and 0≤y≤1.0 are superconducting. Increasing y=2x, both the hole concentration in the Cu2O layers and TcR=0 increases to a maximum value of 0.349 and 78 K at x=0.4 and y=0.8, respectively. A correlation between the Tc and hole concentration seems to hold.

The structural and superconducting properties of series of (La2−xYx)Ba2(CayCu4+y)Oz (La-2125); 0.0 0.0 , compounds having tetragonal triple perovskite structure and maximum Tc of 78 K for x=0.4 (y=2x) , are investigated using X-ray diffraction, susceptibility, resistivity and oxygen content measurements. It is observed that, both oxygen content and hole concentration (p) increase as the samples are doped with higher concentration of Ca2+ and Tc increases with increasing y=2x as p increases upto an optimum level of 0.349 at x=0.4. Thus by adding equal amounts of CaO and CuO alongwith Y3+ for La3+ in La2Ba2Cu4Oz (La-224) semiconductor, superconductivity occurs. The addition of Ca is turning on a mechanism which affects both hole concentration and Tc in a closely related way to that of YBa2Cu3O7−δ (Y-123).