Kenzo Nagase

Over-doping of Tl2Ba2CuO6 due to charge transfer Tl3−t-(Cu-O)p

Abstract Superconductivity was observed in La substituted Tl 2 Ba 2 CuO 6 . Both T c and unit cell dimension, a , increase with increasing La concentration, indicating that an over-doping state in Tl 2 Ba 2 CuO 6 , which was due to charge transfer Tl 3− t -( Cu - O ) p as supported from XPS measurements, was relieved by La substitution for Ba.

Systematics on the thermal reactions of lanthanide malonates Ln2(C3H2O4)3 · nH2O in the solid state

Abstract The thermal reactions of the lanthanide malonates in the solid state were investigated systematically by means of TG/DTA, and X-ray, IR and elemental analyses. The onset temperatures of the dehydration ( t h ) and decomposition ( t d ), which can measure relative stabilities of the hydrated and anhydrous malonates, respectively, varied systematically with some physical parameters of the lanthanides and lanthanide malonates.

Thermogravimetric studies of the over-doping state of Tl2Ba2CuO6−δ due to charge transfer

Abstract Variation of the T c of Tl 2 Ba 2 CuO 6−δ (2201) was demonstrated under various synthesis conditions: annealing atmosphere and quenching temperature. The oxygen vacancy (δ) was determined precisely by thermogravimetric analysis in oxygen and nitrogen atmospheres. The nonsuperconducting phase (δ⋍0) in Tl 2 Ba 2 CuO 6−δ due to charge transfer Tl 3− t -(Cu-O) p was turned into a superconducting state by the introduction of a small amount of oxygen vacancies (δ>0). The highest T c value of 85 K was achieved with an optimum value of δ⋍0.15 by annealing at 600°C in a nitrogen atmosphere.

Iodometric determination of oxygen contents of the T1 single layer system and their relevance to superconductivity

Abstract The oxygen contents of oxygen-annealed T1 single layer systems were determined by iodometric titration. The oxygen contents, w , of T1Ba 2 Ca 1- x Y x Cu 2 O w increased with Y concentration, x , substituted for Ca. Oxygen vacancy, y , was estimated to be about. y =0.3 in oxygen-annealed T1Ba 2 Ca n -1 Cu n O 2 n +3- y ( n =2, 3, 4). The Cu valence of oxygen-annealed T1Ba 2 Ca n -1 Cu n O 2 n +3- y is calculated to be about 2.2+, if the hole is introduced only in the CuO 2 pyramidal sheets. Square planar CuO 2 planes of the T1 single layer system may not be active for superconductivity.

Thermal decomposition of bivalent transition metal malonates in various atmospheres

Abstract The thermal decomposition of the malonates of bivalent transition metals (Mn, Fe, Co, Ni, Cu and Zn) was investigated by mainly TG-DTA, X-ray diffraction analysis and evolved gas analysis in atmospheres of N 2 , CO 2 and O 2 and in the air. It was shown that CO 2 has an inhibiting effect on the decomposition whereas O 2 and air have the accelerating effects on the basis of N 2 . The decomposition of the salts investigated can be classified into three groups from solid decomposition products: Mn and Zn malonates gave the metal oxides including 1–1.5 moles of elementary carbon, while Cu and Ni malonates gave the metals with 1–1.5 moles of the carbon. Fe and Co malonates in the last group gave once the metal oxides with 1-0.5 moles of the carbon and the oxides produced were subsequently reduced to the metals by the carbon. A possible reaction mechanism for the malonates was discussed and compared with those of the corresponding oxalates and succinates.

Thermal decomposition of Fe(II) carboxylates: Comparison of decomposition processes between the formate and malonate

Abstract The thermogravimetric curves of Fe(II) formate dihydrate, Fe(for)2 · 2H2O, and Fe(II) malonate dihydrate, Fe(mal) · 2H2O, in an argon atmosphere were obtained. The products at each decomposition stage were determined by Mossbauer spectroscopy, IR, powder X-ray analysis and gas chromatography. The dehydration of Fe(for)2 · 2H2O took place in two steps to form an anhydrous salt in the crystalline state, while Fe(mal) · 2H2O lost 2 mole of H2O in one step to form an anhydrous salt in the amorphous state. The decomposition processes of Fe(for)2 and Fe(mal) were represented as Fe(for)2→Fe3O4→FeO and Fe(mal)→FeO→α-Fe, respectively.

Structure and superconductivity of Tl0.5Pb0.5Sr2CuOy

Abstract The structure and superconductivity of Tl 0.5 Pb 0.5 Sr 2 CuO y were studied by controlling the oxygen content or partially substituting lanthanide ions for Sr(II). The crystal structure greatly changed with the oxygen content. The samples with nearly full oxygen content ( y ∼5.0) had tetragonal symmetry, while those with the lowest oxygen content ( y ∼4.3) showed orthrhombic symmetry. The c -dimension increased for y >4.8 and then decreased with decreasing oxygen content, while the a -dimension was almost independent of composition. On the other hand, in the case of lanthanide substitution, the a - and c -dimensions were increased and decreased respectively with increasing lanthanide content. Superconductivity appeared with the substitution of a small amount of lanthanide ions for Sr(II), but was never achieved by controlling the oxygen content.

Spectrophotometric and thermal analytical studies on the dehydration of copper(II) sulfate and its double salts

Abstract Spectrophotometric (diffuse reflection) and TG-DTA data on the dehydration of CuSO 4 · 5H 2 O, Na 2 Cu(SO 4 ) 2 · 2H 2 O, M 2 Cu(SO 4 ) 2 · 6H 2 O(M + = K + , Rb + , Cs + and NH + 4 ) and Co 2 Cu(SO 4 ) 3 · 18H 2 O are given. Although complete dehydration of CuSO 4 · 5H 2 O brings about a striking color change from blue to white, it was found that there is only a slight decrease in the v max. of its d-d band in the course of this change, and the total light absorption in the visible-UV region increases at the same time. The dehydration of the alkali metal and ammonium double salts, most of which contain [Cu(OH 2 ) 6 ] 2+ aquo ions (in contrast to the [Cu(OH 2 ) 4 ] 2+ in CuSO 4 · 5H 2 O), occurs generally more easily than that of CuSO 4 - 5H 2 O, and their v max. increases slightly in the change, leading to blue or green anhydrous products, although the formation of a white modification was observed with the potassium salt. It was also found that the v max. of the Cu 2+ ion in the dehydrated cobalt(II) double salt is still lower than that in anhydrous CuSO 4 , i.e., the ligand field and/or tetragonality around it is decreased by the presence of Co 2+ ions.

Superconductivity in the overdoping state of the (Hg,Tl)(Ba,La)2CuOυ and (Hg,Tl)2Ba2CuOν systems

Abstract The effect of Tl substitution for Hg in the HgBaCuO system has been investigated for a wide substitution range. The Tl substitution range of the single and double (Hg,Tl) layer systems was observed for 0–50% and 50–100%, respectively. Both the single and double (Hg,Tl) layer phases show the temperature dependence of resistivity of the metallic normal state and the overdoping state is confirmed by the substitution of Ba with La where the Tc increases with increasing La concentration. The Tc of the single (Hg, Tl) layer system, Hg1−xTlxBa2CuOυ, decreases with increasing Tl concentration and becomes non-superconducting for x ≧ 0.4 . The double (Hg, Tl) layer system, Hg2−zTlzBa2CuOυ, is non-superconducting due to the overdoping state.

Effects of heating rate (1–300° h−1) on the non-isothermal thermogravimetry of CuSO4 · 5 H2O

Abstract The course of the reaction CuSO4 · 5 H2O − CuSO4 · H2O + 4 H2O was studied by non-isothermal thermogravimetry with various heating rates ranging from 1 to 300° h−. The measurements were made either in static air, in a dry nitrogen stream, or in water vapor at a reduced pressure (9 mm Hg). In static air, the shape of the TG curve changed drastically at a heating rate of 13 to 15° h−, and this change was explained by considering the nature of the plateaus and inflections present. In a dry nitrogen stream, the dehydration is made much easier at slow heating rates and occurs almost in one step at 2° h−; in water vapor at 9 mm Hg, on the other hand, a very distinct two-step curve is obtained at 1° h−. This can reasonably be compared with the phase diagram of copper sulfate.