Y. Babu

Chemical incorporation of fluorine into YBa2 Cu3O6.5+δ

Abstract Evidence of incorporation of fluorine into the lattice of 1,2,3,7 orthorhombic superconducting oxide by a reaction of this compound with NH4HF2 at 600K is presented. While TG/DTA data give clue to the reaction between the two, XRD of the product shows a broad peak around 2Θ=26° which disappears on heating to 1000K giving BaF2 peaks. The product with four F atoms in place of two O atoms shows Tc close to that in the virgin orthorhombic oxide.

Application of ICAP-AES for the determination of Dy, Eu, Gd, Sm and Th in uranium after chemical separation.

A method has been developed for the determination of Dy, Eu, Gd, Sm and Th in uranium (after chemical separation) by use of an inductively-coupled argon plasma in conjunction with a direct-reading spectrometer. The method can be used for the determination of Dy and Eu down to 0.02 mug ml , Gd to 0.05 mug ml , Sm to 0.1 mug ml and Th to 0.20 mug ml .

Orienting effect of magnetic field on some copper metallomesogen powders: single crystal-like alignment

Abstract EPR spectra of some powdered metallomesogens cooled in magnetic fields of 0.3/1.2 T showed at 77 K, a distinctive change in line shape from that at room temperature (RT), indicating appearance of field-induced alignment. However, conformation and length of the chains have to match the packing requirement. Thus, the closed packed C 7 Cu shows 100% alignment, whereas C 11 OCu/C 9 OCu show only partial alignment. These have a tendency to self-assemble into random domains in the polycrystalline solid at RT, which tend to orient themselves along the magnetic field at 77 K. This is the first report of a dry paramagnetic powder, showing a single crystal-like alignment along H at the high temperature of 77 K.

Microwave absorption studies in new high-Tc superconducting oxide systems: Tl-Ba-Ca-Cu-O and Bi-Ca-Sr-Cu-O

Microwave absorption studies of the new high-Tc superconducting systems Tl-Ba-Ca-Cu-O (Tc( rho =0)=118 K) and Bi-Ca-Sr-Cu-O (Tc( rho =0)=84 K) were conducted using an X-band EPR spectrometer. The main features observed were (i) a sharp change in the leakage current at Tc; (ii) intense low-field (<50 G) absorption below Tc; and (iii) a largely field-independent absorption, the intensity of which was found to increase with increasing external magnetic field strength up to 10 kG. The dependence of the intensity on magnetic field is explained in terms of magnetic-field-induced decoupling of grains and field, and temperature-dependent lambda MW/ lambda , where lambda MW is the microwave penetration depth and lambda is the London penetration depth.

Photoacoustic response of CdS quantum dots in nafion

Quantum confinement effects on the excitonic transitions in CdS quantum dots embedded in the polymer matrix Nafion are studied using the technique of photoacoustic spectroscopy. The characteristic blueshift in the absorption onset with decreasing quantum dot size is in agreement with that observed in the optical absorption spectra. Excitonic transitions are better resolved in the photoacoustic spectra when compared to the corresponding optical absorption spectra. The results are discussed in relation to existing theoretical models.

Electrothermal AAS studies of Sm, Eu, Dy, and Er separated from uranium

ZusammenfassungDie Untersuchungen wurden mit Hilfe des Graphitrohrofens nach Maßmann durchgeführt. In folgenden Bereichen ergaben sich lineare Eichkurven: Sm 1–10 μg/ml, Eu 0,05–0,6 μg/ml, Dy 0,1–0,8 μg/ml, Er 0,1μ-1,0 μg/ml. Die aus synthetischen Proben erhaltenen Ergebnisse stimmten gut mit den durch Emissionsspektrographie erhaltenen überein. Versuche wurden mit Röhren mit pyrolytischen Kohlenstoffüberzug mit und ohne Vorbehandlung durch La, Ta und Y durchgeführt und ergaben eine bis 15%ige Steigerung durch die Behandlung sowie eine mäßige Besserung des Memoryeffektes. Eine Behandlung mit Ta war besonders für Sm vorteilhaft. Störungen durch andere Lanthanide waren vernachlässigbar. Uran beeinflußte jedoch die Absorption. Im Falle von Eu zeigte sich nach anfänglicher Zunahme fast eine Unabhängigkeit, während bei den anderen untersuchten Elementen nach anfänglicher Zunahme eine beträchtliche Abnahme auftrat. Mit Eu, Dy und Er wurde ebenfalls die Temperaturabhängigkeit der Absorption untersucht. Festgestellte Unterschiede im Verhalten werden auf unterschiedliche Atomisierung zurückgeführt.SummaryStudies were conducted on the assay of Sm, Eu, Dy and Er separated from uranium using aqueous standards by electrothermal AAS with Massmann type graphite furnace. The working curves were found to be linear in the ranges Sm (1–10 μg/ml), Eu (0.05–0.6 μg/ml), Dy (0.1–0.8 μg/ml) and Er (0.1–1.0 μg/ml). The values obtained for synthetic samples agreed favourably with those obtained by emission spectrographic method. Experiments using pyrolytic carbon coated tubes with and without pretreatment by La, Ta and Y have shown an enhancement with treatment upto a maximum of 15% and improve the memory effect marginally. The effect of Ta treatment was found to be singularly useful in improving the general behaviour of Sm. The interference effects of lanthanides, other than the analyte, were found to be negligible. However, the presence of uranium was found to affect the absorbance. The absorbance of Eu was found to be nearly independent of uranium after an initial increase. On the other hand, the absorbance of other elements studied was found to drastically decrease after an initial enhancement. Detailed investigations of temperature dependence of absorbance were carried out using Eu, Dy and Er. The differences in the behaviour of these elements is attributed to probable differences in the modes of their atomization.

A new and sensitive method for detection of superconductivity using microwave bridge

Abstract It is shown that a four arm microwave bridge used in conventional x-band electron paramagnetic resonance (EPR) spectrometers with the sample loaded in the cavity arm can be very effectively used for monitoring the superconducting transition in high T c oxides. The experiments involve monitoring the leakage current (a measure of imbalance of the bridge) as a function of sample temperature. Experiments using a number of well characterised 1-2-3-7 oxides have shown sharp drop in leakage current at T c . The data obtained show a clear analogy between the temperature dependence of resistivity and that of leakage current.

Unique signatures of microwave absorption of superconducting YBa2Cu3O7−x

Abstract Microwave absorption in the 9 GHz range using EPR technique in the superconducting phase of YBa 2 Cu 3 O 7− x and related compounds has been investigated as a function of temperature and magnetic field. The microwave absorption in the superconducting phase is found to occur due to three different processes. These are manifested in the observation of: (i) An intense low field absorption, (ii) a field-independent absorption and (iii) an absorption-like feature in the intensity versus temperature plot in the close vicinity of T c . This feature appeared more prominently when the sample was cooled at high (∼few KG) magnetic fields. The low field absorption had exhibited saturation behaviour with increasing microwave power and temperature dependent line position. These are some of the features normally observed for ‘resonance’ absorptions. The field-independent absorption is identified as due to the imaginary part of the a.c. diamagnetic susceptibility of superconducting YBa 2 Cu 3 O 7− x . The mechanism for the third process is not yet understood.

Direct determination of metallic impurities in graphite by EDXRF

Energy dispersive X-ray fluorescence (EDXRF) methods have been developed for the direct determination of 14 trace metallic impurities in graphite powder without any need for sample dissolution. Using synthetic standards, calibration curves were established for different elements after optimizing the spectrometer parameters. Two synthetic samples were analyzed to evaluate the performance of the developed analytical methods. The estimates for most of the analytes were in good agreement with the added amounts. Three graphite powder samples were analyzed by the present method as well as by D.C. arc emission spectrometric technique for comparison and the agreement between the analyte values determined, using both methods was good. Samples in pellet form were analyzed using a separate calibration with standards in pellet form. The present method is rapid, as it alleviates the need for any chemical treatment and gives good precision.

EPR and ENDOR studies of self(α)-irradiation effects in Pu(VI) oxalate: evidence for participation of 5f electrons of 239Pu in chemical bonding with CO2−

Abstract EPR and ENDOR investigations have been carried out on polycrystalline samples of self( α )-irradiated PuO 2 C 2 O 4 ·3H 2 O (cumulative dose = 1 MGy). The 239 Pu ( I =1/2) hyperfine structure on the EPR signal of the CO 2 − radical ion has given clear evidence for participation of 5f electrons of 239 Pu in chemical bonding. The ENDOR spectra were used to identify unambiguously the hyperfine interaction between the unpaired electron on the CO 2 − radical ion and the nuclear spin of 239 Pu. In addition to the CO 2 − radical ion, EPR evidence was also obtained for the formation of O 2 − during the autoradiolysis of PuO 2 C 2 O 4 ·3H 2 O.