E. P. Khlybov

Crystal structure of Ru(Sr, Gd)2(Gd, Sr)Cu2O8 and Ru(Sr, Eu)2(Eu, Ce)2Cu2O10 phases

Abstract We have investigated the synthesis, crystal structure, resistivity and magnetic measurements of phases in the Ru(Sr,Gd) 2 (Gd,Sr)Cu 2 O 8− δ (Ru-1212) and Ru(Sr,Eu) 2 (Eu,Ce) 2 Cu 2 O 10− δ (Ru-1222) systems. Rietveld refinement of the structure was carried out. The refined compositions before and after oxygen treatment are Ru 1.00(1) (Sr 1− y Gd y ) 2 (Gd 1− z Sr z )Cu 2 O 8 ( y =0.03(1), z =0.19(1)) (Ru-1212; T c 1− x Cu x )(Sr 1− y Gd y ) 2 (Gd 1− z Sr z )Cu 2 O 8 ( x =0.05(1), y =0.02(1), z =0.16(1)) (Ru,Cu-1212; T c 1− x Cu x )(Sr 1− y Eu y ) 2 (Eu 1− z Ce z )Cu 2 O 10 ( x =0.04(2), y =0.09(2), z =0.44(3)) (Ru,Cu-1222; T c 1− x Ce x )(Sr 1− y Eu y ) 2 (Eu 1− z Ce z ) 2 Cu 2 O 10 ( x =0.08(2), y =0.15(2), z =0.25(3)) (Ru,Ce-1222; T c(onset) =40 K, T c(zero) =12 K). Ruthenium atoms in these structures are octahedrally coordinated as the (Ru 5+ O 6 ) 7− species. The formal charge of Cu (FC Cu) calculated from the electroneutrality condition of refined phase composition increases after oxygen treatment and achieves an optimal value (FC Cu∼2.14) for the superconducting (Ru,Ce)-1222 phase ( t =1000°C, p =1 GPa, τ =72 h).

Synthesis, crystal structure and properties of superconducting and non-superconducting RuSr2(Nd,Ce)2Cu2O10 phases»

Abstract In this paper we report on the structural, electrical and magnetic properties of a systematic work performed on the synthesis of RuSr 2 (Nd,Ce) 2 Cu 2 O 10− δ (Ru-1222) samples that differ for the number of annealings or sintering temperature in oxygen. This is done in order to highlight the different behaviours of properties as a consequence of the treatments. In particular, we deal with the development or loss of superconductivity after oxygen treatment. Further we discuss the influence of phase composition on superconductivity and magnetic ordering.

Crystal structure of In-based cuprates: (In,Cu)S2YCu2O6+δ (1212), (In,Cu)(Sr,Ho)2(Ho,Ce4+)2Cu2O8+δ (1222)

Abstract The indium-based cuprates with perovskite-like structure (In,Cu)Sr2YCu2O6+δ and (In,Cu)(Sr,Ho)2(Ho,Ce)2Cu2O8+δ, belonging to the homologous series (In,Cu)(Sr,Ln)2(Ln,Sr)k−1CukO2k+2+δ with k=1 (In,Cu-1212) and (In,Cu)(Sr,Ln)2(Ln,Ce)k+1Cu2O2k+6+δ with k=1 (In,Cu-1222) have been obtained. Their structure has been refined at room temperature using X-ray powder diffraction data. The samples with the nominal compositions (In0.5Cu0.5)Sr2YCu2Ox and (In2/3Cu1/3)(Ho1/3Ce2/3)3Sr2Cu2Ox appeared to contain phases with lattice parameters a=3.8163(1), c=11.9785(6) A (In,Cu-1212, sp. gr. P4/mmm) and a=3.8272(0), c=29.0774(3) A (In,Cu-1222, sp. gr. I4/mmm), respectively. Rietveld refinements were carried out. The real composition of these phases may be written as (In0.89Cu0.11(3))Sr2YCu2O6.98(4) (In,Cu-1212) and (In0.98Cu0.02(1))(Sr1.25Ho0.75(2))(Ho1.89Ce0.11(5)4+)Cu2.00O9.00 (In,Cu-1222). The refined composition of these phases after oxygen treatment was formal to be (In0.82Cu0.18(2))Sr2YCu2O7.00 (In, Cu ∗ -1212) and (In0.87Cu0.13(1))(Sr1.52Ho0.48(2))(Ho1.95Ce0.05(3)4+)Cu2O9.00 (In,Cu ∗ -1222). The Cu formal charge (FC Cu) in the (In,Cu)-1212, calculated from electroneutrality condition of the refined phase composition, was almost the same as before (FC Cu∼2.04) and after (FC Cu∼2.09) the oxygen treatment (underdoped phase). On the contrary, the FC Cu for the (In,Cu)-1222 increased after oxygen annealing (from −2.08 to −2.30) (overdoped phase). The non-optimal values of the Cu formal charge could be a possible reason for the absence of superconductivity in these samples.

Ruthenium-Based Perovskitelike Phases: Synthesis, Structure, and Properties

This paper reports on synthesis and X-ray diffraction study of two groups of phases obtained from batch mixtures: (La,Srk+1(Ru,Cu)kO3k+1 and (La,Sr)3(Ru,Cu)3O6+δ (group I); RuSr2LnCu2O8−δ (Ln = Nd for the first time, Sm, Eu, Gd, (Gd,Y) for the first time), RuSr2(Ln,Ce4+)2Cu2O10−δ (Ln = Pr and Nd for the first time, Sm, Eu, Gd, (Gd,Y) for the first time), and (Ru,Cu)Sr2(Ln,Ce4+)2Cu2O10−δ (Ln = Tb and Y for the first time) (group II). In group I, phases with K2NiF4, Sr3Ti2O7, and cubic perovskite type structures are typically formed; in group II, these are respectively (Ru,Cu)(Sr,Ln)2(Ln,Sr)Cu2O8−δ (1212 type), (Ru,Cu)(Sr,Ln)2(Ln,Ce4+)2Cu2O10−δ (1222 type), and cubic perovskite type structures (the content of the latter depends on the type of Ln). Variation of the formal charge (f.c.) of Ru (group I) and Cu (group II) was evaluated in relation to the cation composition of the phases (groups I and II) and the content of superstoichiometric oxygen (group II). Phases of 1222 type with Ln = Nd, Sm, Eu, Gd, and (Gd,Y) and phases of 1212 type with Ln = Gd exhibited superconducting properties with Tc max ∼ 40 K.

Solid solutions (Ru,Nb)Sr2(Sm1.4Ce0.6)Cu2O10−δ: Synthesis, structure, and properties

Solid solutions of as-batch composition (Ru1−xNbx)Sr2(Sm1.4Ce0.6)Cu2O10−δ (the Ru,Nb)-1222 phase), where x = 0.0, 0.25, 0.50, 0.75, or 1.00, have been synthesized and characterized by X-ray diffraction. A correlation is proposed between the refined composition of the Ru-1222 and Nb-1222 phases and their structural features. With increasing oxygen concentration in the Ru-1222 phase, the superconducting transition temperature increases from Tc = 28 to Tc = 34 K. The composition and magnetic properties of the Ru-1222 phase are affected by the batch composition: unlike in Ru + RuO2 mixtures, the presence of ruthenium in the batch decreases the oxygen proportion and increases the magnetic ordering temperature Tm; the phase of as-batch composition NbSr2(Sm1.4Ce0.6)Cu2O10−δ is paramagnetic.

Dependence of the Structure and Properties of (M,Cu)Sr2(Ln,Ca)Cu2O8−δ (1212) and (M,Cu)Sr2(Ln,Ce4+)2Cu2O10−δ (1222) Phases on the Cation M

The composition and structure of (M,Cu)(Sr,Ln)2(Ln,Ca,Sr)Cu2O8−δ phases, where M = B, Al, Cr, Pb, Bi, Ru, or Mo (1212 type), and (M,Cu)(Sr,Ln(2(Ln,Ce4+)2Cu2O10−δ phases, where M = V, Cr, Mn, Ru, or Mo (1222 type), have been determined. The role of the M cation in the formation of the crystal structures and the superconductivity phenomenon was analyzed. The relationship between the type of M cation and structural parameters was discovered.

Crystal Structure of (Cr,Cu)(Sr,La)2(La,A)Cu2O8-δ (1212-type) and (Cr,Cu)Sr2(Y,Ce)2Cu2O10-δ (1222-type) Phases

Conditions of the synthesis, crystal structures, mechanical properties, electrical resistivities and magnetizations of cuprates with the general formula (Cr,Cu)(Sr,La) 2 (La,A)Cu 2 O 8-δ where A=Ca or Sr of 1212-type and (Cr,Cu)Sr 2 (Y,Ce) 2 Cu 2 O 10-δ of 1222-type were investigated. The compositions of the cuprates and an amount of the impurity phases in the samples were determined. Rietveld refinement of the structure was carried out. It was found that the formal charges of Cu (FC Cu ) calculated from the electroneutrality of refined phase compositions do not achieve value optimal for the appearence of superconducting phases.

Indium Perovskite-Like Phases: Synthesis, Crystal Structure Refinement, and Properties

This paper describes syntheses and structure and composition refinement for phases of the general composition (In,Cu)Sr2YCu2O6 + δ (1212) and (In,Cu)(Sr,Ho)2(Ho,Ce)2O8 + δ (1222) obtained in air atmosphere and for the same phases treated in oxygen. Oxygen treatment did not change the oxygen content in the phases, but changed the composition of the cationic (especially In) sites. The absence of superconductivity is explained by the nonoptimal values of the formal charge of copper [FC(Cu)] obtained from the electroneutrality condition and taking into account the refined phase compositions. Superconductivity found for the phase of composition (In,Cu)Ba2(Y,Ca)Cu2O6 + δ (Tc = 80 K) is lost when the sample is annealed in air and during subsequent thermobaric treatment, leading to changes in the oxygen and indium contents and to a decrease in FC(Cu) from ∼2.15 to 2.05 and 2.08, respectively.