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Reports a series of thermoelectric power studies on Nd[sub1.82-x]Sr[subx]Ce[sub0.18]CuO[suby]:x≤0.18 superconductors. Experiments; Results; Conclusions.

Presents a study which examined the magnetically ordered valence fluctuating compound samarium ruthenium tin[sub3]. Methods; Results; Discussion.

Reports the magnetic properties of the rare-earth intermetallic compounds, Gd[sub2]Ni[sub3]Si[sub5] and Sm[sub2]Ni[sub3]Si[sub5]. Experimental details; Structure description; Magnetic and resistivity measurements; Conclusion.

The Cu K-edge measurements on the optimum Tc 1201 compounds (Hg1− xM x)Sr2CuO4+δ (M = Cr, Mo, or Re; 0.10 ≤ x ≤ 0.30) show besides Cu2+ (predominant) a very weak but distinct signature of Cu1+, only in the superconducting (SC) samples. The Cu1+ feature is conspicuously absent when these compositions are non-superconducting because of different processing conditions. Our finding of monovalent Cu in SC (Hg,M)/Sr-1201 favors the presence of Cu at the Hg-site and this seems to facilitate superconductivity in these cuprates. [ABSTRACT FROM AUTHOR]

Chemically stable nominal compositions of (Hg1- xRe x)Sr2CuO4 + δ ( x = 0.05, 0.10, and 0.20), designated as (Hg,Re)-1201 phase, were synthesized at ∼920°C in partial vacuum. The samples with x = 0.05 and 0.10 are superconducting (SC) with Tc onset ∼40 and ∼54 K, respectively. On the other hand, for the composition with x = 0.20, the sample is nonsuperconducting down to 5 K. The sample with composition (Hg0.9Re0.1)Sr2CuO4 + δ on cooling, below 10 K in dc-field of 4 kOe, shows a dramatic decrease (reversal) in diamagnetic signal. Such a reduction in diamagnetic response is also reflected by the sample's supercurrent induced magnetic hysteresis curve generated at 9 K. In the light of the available reports and our Re LIII-edge measurements, we attribute this effect to a field enhanced paramagnetic contribution probably arising mainly from mixed valent (6+, 7+ dominant) Re ions. The critical current density ( Jc), calculated using Bean's model, for (Hg0.9Re0.1)Sr2CuO4 + δ is ∼6 × 103 A/cm2 (4.5 K, 5 kOe). [ABSTRACT FROM AUTHOR]

The nominal (Hg0.7Cr0.3)Sr2(Ca0.7Y0.3)Cu2O6 + δ, referred to as (Hg,Cr)-1212, were successfully synthesized at high temperature in partial vacuum. The samples were subsequently annealed in Ar or O2 annealed at 300°C under ambient pressure. No Tc was observed in any of these samples down to 12 K which is in contrast to high pressure synthesized Y-free (Hg,Cr)-1212 phase where the latter exhibits a superconductivity at ∼80 K. The divalent state of Cu, as shown by XANES in the as-prepared (Hg,Cr)-1212, is not affected either by Ar or O2 annealing. Depletion of holes due to trivalent Y substitution at the Ca-site, and a relatively higher ' a' lattice parameter (≥3.851 Å) are the apparent reasons for the non-superconducting nature of the samples. [ABSTRACT FROM AUTHOR]

Superconducting (Hg1− xCr x)Sr2CuO4+δ, x ∼ 0.36, samples of 1201-type, synthesized in partial vacuum, show Tc onset of ∼58 K, Tc ( R = 0) ∼52 K. It is found that Tc is not affected by the subsequent Ar or O2 annealing treatment. Remarkably, the annealed samples show significant improvement in the diamagnetic signal. Hg L3-edge measurements on 1201 samples show divalent state of mercury. The Cu K-edge spectra for the samples, after taking due account of the impurity phases, show noticeable modifications in the split main peak features on Ar or O2 annealing, suggesting changes in the crystal field asymmetry. In the superconducting (SC) samples, a weak but distinct signature of Cu1+ is seen. The Cu1+ feature is absent in all the non-SC 1201 samples as well as in the impurity phase SrCuO2 and Sr2CuO3 samples. An attempt is made to explain the observed Cu1+ feature in SC (Hg,Cr)-1201 in the light of the available reports. [ABSTRACT FROM AUTHOR]

In continuation of our recent work [1] on superconducting 1201-type (Hg,M)Sr2CuO4+δ, M = Cr system, the samples of (Hg1− xM x)Sr2CuO4+δ, M = Mo ( x = 0.15, 0.25, and 0.30), were synthesised in partial vacuum. The x = 0.15 composition shows a maximum Tc onset of ∼66 K, while x = 0.25 exhibits Tc onset of ∼50 K. For x = 0.30 sample, the observed Tc onset of ∼36 K is discretely different from the reported values of 20 and 58 K. X-ray absorption measurements on (Hg,Mo)-1201 samples show Hg in divalent state and Cu predominantly in Cu2+ state. A weak but distinct Cu1+ signature is also observed in the SC (Hg,Mo)-1201 samples, which is absent in the impurity SrCuO2 and Sr2CuO3 phases. On the basis of available reports, it is viewed that Cu1+ can arise because of a small fraction of Cu occupying the Hg site in (Hg,Mo)-1201 system. [ABSTRACT FROM AUTHOR]

The 1201-type nominal (Hg[sub 0.9]Re[sub 0.1])Sr[sub 2]CuO[sub 4+δ] samples, synthesized at ∼920°C in partial vacuum, show, from temperature dependent dc-magnetization, T[sup onset, sub c] ∼54 K. The CuK-edge features obtained from X-ray absorption measurements on the sample show predominantly Cu[sup 2+] state and a weak but distinct Cu[sup 1+] signature due to superconducting 1201 phase (after taking due account of impurity Sr[sub 2]CuO[sub 3], and SrCuO[sub 2] phases). The presence of Cu[sup 1+] signature in SC samples is consistent with our earlier observations of Cu[sup 1+] in Ba-free superconducting (Hg,Cr)-1201 and (Hg,Mo)-1201 materials. [ABSTRACT FROM AUTHOR]

Beta barium borate (β-BBO) crystals have been grown by the top seeded solution growth technique (TSSG) using Na2O as a flux. The crystals exhibited high transparency and the absence of inclusions and found to have sodium contamination in the range 150 to 230 p.p.m. The effect of this contamination on some crystal properties of interest has been investigated. The presence of impurities causes optical absorption below 550 nm in BBO crystals of both α and β-phases. X-ray photo emission spectroscopy (XPS) measurements performed on these crystals show that sodium gives rise to a measurable shift in the binding energies of the constituent ions. Further, the results show that Na+ ions enter into the lattice substitutionally and provide charge trapping sites close to the band edge. [ABSTRACT FROM AUTHOR]

The effect of tetravalent Zr substitution (≤2 at%) at the Cu site in T'-type Nd[sub 2-x]Ce[sub x]CuO[sub 4-δ] (NCCO), x = 0.12, 0.14, 0.15, on the superconducting (SC) behavior is investigated. EDX analyses of the samples clearly reveal the presence of only ∼0.5 at% Zr in the T'-phase. Irrespective of the Ce content (0.12 ≤ x ≤ 0.15), T[sub c] is found to depress with Zr. A fall in T[sub c] of ∼2 K is observed due to 0.5 at% Zr[sup 4+] in x = 0.14 samples, while the NCCO (x = 0.12) on substitution of Zr (expected to dope 2 electrons per Zr[sup 4+] and induce superconductivity) remains non-SC. The reported conjecture regarding T[sub c] inducement due to the carrier addition of 0.03 (per formula unit) arising from 3 at% In[sup 3+] (or Ga[sup 3+]) substitution for Cu in Nd[sub 1.88]Ce[sub 0.12]CuO[sub 4-δ] [Ayoub et al., Physica C170, 211 (1990); Felner et al., Phys. Rev. B40, 11366 (1989)] is not applicable for the Zr-substituted NCCO. [ABSTRACT FROM AUTHOR]

Presents information on a study which investigated the dilute substitution of cerium (Ce) by yttrium and gadolinium in Ce[sub2]Ni[sub3]Si[sub5]. Concept of Kondo holes; Temperature dependence of the intensity of the two edges; Valence fluctuation nature of Ce in Ce[sub2]Ni[sub3]Si[sub5].

Presents an abstract of the study 'Thermoelectric Power Studies of a Nd[sub1.82-x]Sr[subx]Ce[sub0.18]CuO[suby] Superconducting System,' by Okram G. Singh, B.D. Padalia, Om Prakash, V.N. Moorthy and Anant V. Narlikar.

A versatile soft x-ray appearance potential spectrometer with UHV and several other facilities has been designed and constructed using HAMAMATSU-make Cu-BeO photoelectron multiplier for the detection of soft x rays. Salient features of the design and construction aspects of the instrument and its performance are discussed. [ABSTRACT FROM AUTHOR]