In comparison to the Y1−xPrxBa2Cu3O7−δ (Y/Pr-123) system the influence of the substitution of Pr for Y on the structural and superconducting properties of the Y1−xPrxBa2Cu4O8 (Y/Pr-124) system was investigated. Among the different reaction procedures for the synthesis at ambient oxygen pressure a technique involving the crystallization from the quenched melt was employed for the first time. In analogy to the Y/Pr-123 system the Pr substitution leads to an increase of the unit-cell parameters and to a successive suppression of superconductivity in Y/Pr-124 with a critical Pr concentration xcr of 0.75 which is higher than that of 0.56 for Y/Pr-123. The normal-state behavior of the Y/Pr-124 samples could be described by a Curie-Weiβ law, yielding effective Pr moments of about 2.5μB that correspond to a Pr valence of 4+. Different from the Y/Pr-123 system, the Curie-Weiβ temperature θ was found to be positive for the superconducting and negative for the normal samples, whereas in Y/Pr-123 θ was always negative.

Before investigating the ternary system Bi2O3-CaO-CuO, a revision of the binary bounding system Bi2O3-CaO was first necessary. In the range between 20 and 70 mol % CaO the solid solutions β and α′'1 and the stoichiometric compounds Bi2CaO4, Bi6Ca4O13, and Bi2Ca2O5 were found to exist for 675 °C≦T≦780 °C. Above 780 °C a new high temperature compound with the formula Bi6Ca5O14 has been identified. The X-ray powder diffraction data, unit cell dimensions, as well as the space group, have been reported. The ternary system contains no intermediate compounds and also no solubility was found for the binary bounding phases. Below 780 °C all the Bi-Ca oxides mentioned above are in equilibrium with CuO. At 820 °C, a wide liquidus field is dominating so that these quasibinary equilibria disappear. For 780 °C<T<820°C the new compound Bi6Ca5O14 forms an equilibrium with Ca2CuO3 and CuO. Other equilibria are deduced. For a fixed ternary composition the reaction path of the sintering process was investigated as a function of time and temperature.

It is first demonstrated experimentally that there are two different irreversibility temperatures, Tirrcer and Tirrgr (Tirrcer(Tirrgr), in high-T ceramic superconductors of the compositions Bi1.6Pb0.3Sb0.1Sr2Ca2Cu2.8Oy and YBa2Cu4O8. At T(Tirrcer, both intragranular and intergranular irreversible currents are induced by pinning. When T)Tirrgr, there are no irreversible currents. It is found that Tirrgr(Tc for bismuth ceramics and Tirrgr approximately Tc for YBa2Cu4O8.

We have investigated, theoretically and experimentally, the penetration of magnetic fields into ceramic HTSC for fields below the lower critical field of the grains. In the framework of a critical state theory in the low-field electrodynamics of a random Josephson medium, expressions for the harmonics of the induction B̄(t) as a function of external parameters were derived for two asymptotic cases — the case of the weak field and the case of the thin sample. The behavior of the magnetic induction B̄ was investigated in AC and DC fields in a wide range of temperature and field amplitudes. Rather good agreement between experimental and theoretical results has been found. From the experimental results the values of number of quantities characterizing the low-field electrodynamics of HTSC and their temperature dependences as well as an explicit expression for the critical current densityjc(H, T) = j0(T)H20(T)H2+H20(T)) were derived.

It was demonstrated that superconducting 124 material can be successfully prepared by using oxide-nitrate-mixtures or nitrate-mixtures with short reaction times at normal oxygen pressure conditions. Small quantities of CuO, BaCuO2 and Y2BaCuO5 could be detected as phase impurities by X-ray diffraction.The best quality samples were prepared using freeze-dryed nitrate solution with Na2CO3 as an accelerator. The amount of impurity phases in these samples was near the detection limit of X-ray diffractometry.

We have investigated experimentally the penetration of low magnetic fields into Bi-based ceramics. The behavior of the harmonics of the induction was investigated in ac and dc fields in a wide range of temperatures and field amplitudes. From the experimental results obtained in the asymptotic case of a weak field the values of a number of quantities characterizing the low-field electrodynamics of HTSC and their temperature dependences as well as an explicit expression for the critical current density jc(H, T)=jo(T)Ho(T)[|H| + Ho(T)] were derived.

physica status solidi (a)Volume 124, Issue 1 p. K59-K62 Short Note Preparation and Magnetic Investigations on MnMoO4 Single Crystals B. Lippold, B. Lippold Sektion Physik der Universität Leipzig Search for more papers by this authorJ. Herrmann, J. Herrmann Sektion Physik der Universität Leipzig Search for more papers by this authorW. Reichelt, W. Reichelt Institut für Anorganische Chemie der Technischen Universität Dresden Search for more papers by this authorH. Oppermann, H. Oppermann Institut für Anorganische Chemie der Technischen Universität Dresden Search for more papers by this author B. Lippold, B. Lippold Sektion Physik der Universität Leipzig Search for more papers by this authorJ. Herrmann, J. Herrmann Sektion Physik der Universität Leipzig Search for more papers by this authorW. Reichelt, W. Reichelt Institut für Anorganische Chemie der Technischen Universität Dresden Search for more papers by this authorH. Oppermann, H. Oppermann Institut für Anorganische Chemie der Technischen Universität Dresden Search for more papers by this author First published: 16 March 1991 https://doi.org/10.1002/pssa.2211240149Citations: 6 Linnéstr. 5, O-7010 Leipzig, FRG. Mommsenstr. 13, O-8027 Dresden, FRG. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume124, Issue116 March 1991Pages K59-K62 RelatedInformation

BaPrO3 orders magnetically at Tc = 11.6 K. The magnetization below Tc behaves like (T-Tc)0.2. Above 25 K the effective magnetic moment per Pr ion was found to be p = 3.34 μB indicating a Pr valence between 3+ and 4+. The paramagnetic Curie-Weiβ temperature θ is −29 K. The magnetically ordered state in BaPrO3 below Tc is supposed to be a ferrimagnetic one. The impurity phase found in PrxY1−xBa2Cu3Oz for x > 0.9 was identified as BaPrO3. It is responsible for the magnetic transition observed in those compounds near 12 K.

Abstract63Cu‐NQR measurements are performed in powdered samples of superconducting YBa2Cu3O7−x (YBaCu) in weak external magnetic fields B0 < 2 mT at temperatures T > Tc (normal conducting state). The NQR‐echo amplitudes exhibit damped oscillations with increasing magnetic field B0. The theoretical evaluation of these oscillations allows the direct determination of the asymmetry parameter η of the electrical field gradient (EFG) tensor and the local magnetic field at the Cu‐sites in the lattice of YBaCu.

physica status solidi (a)Volume 121, Issue 1 p. K91-K94 Short Note Preparation and magnetic investigations on Mn2Mo3O8 single crystals B. Lippold, B. Lippold Sektion Physik der Karl-Marx-Universität Leipzig Search for more papers by this authorJ. Herrmann, J. Herrmann Sektion Physik der Karl-Marx-Universität Leipzig Search for more papers by this authorW. Reichelt, W. Reichelt Sektion Chemie der Technischen Universität Dresden Search for more papers by this authorH. Oppermann, H. Oppermann Sektion Chemie der Technischen Universität Dresden Search for more papers by this author B. Lippold, B. Lippold Sektion Physik der Karl-Marx-Universität Leipzig Search for more papers by this authorJ. Herrmann, J. Herrmann Sektion Physik der Karl-Marx-Universität Leipzig Search for more papers by this authorW. Reichelt, W. Reichelt Sektion Chemie der Technischen Universität Dresden Search for more papers by this authorH. Oppermann, H. Oppermann Sektion Chemie der Technischen Universität Dresden Search for more papers by this author First published: 16 September 1990 https://doi.org/10.1002/pssa.2211210162Citations: 6 Linnéstr. 5, DDR-7010 Leipzig, GDR. Mommsenstr. 13, DDR-8027 Dresden, GDR. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat References 1 W. H. McCarrol, L. Katz, and R. Ward, J. Amer. Chem. Soc. 79, 5410 (1957). 2 L. G. Van Uitert, R. C. Sherwood, H. J. Williams, J. J. Rubin, and W. A. Bonner, J. Phys. Chem. Solids 25, 1447 (1964). 3 D. Bertrand and H. Kerner-czeskleba, J. Physique 36, 379 (1975). 4 P. Strobel, Y. Le Page, and S. P. McAlister, J. Solid State Chem. 42, 242 (1982). 5 U. Wiesner, W. Reichelt, and G. Krabbes, Z. anorg. allg. Chemie 551, 67 (1987). 6 W. Reichelt, H. G. Schmidt, G. Wolf, and H. Oppermann, Jahreshaupttagung der Chemischen Gesellschaft der DDR, Karl-Marx-Stadt 1989. 7 W. Reichelt and H. Oppermann, Z. anorg. allg. Chemie, in preparation. Citing Literature Volume121, Issue116 September 1990Pages K91-K94 ReferencesRelatedInformation

First we studied the kinetics of the formation of Ba monoferrite by means of Mössbauer spectroscopy. The most important result is the considerable portion of hexaferrite existing after treatment of the starting materials between 800 and 900°C, caused by a higher rate of diffusion of the Ba2+ ions in comparison to the Fe3+ ions.