Preparation and Characterization of (1 — x) Pb(Mg1/3Nb2/3) O3 — x PbTiO3 Electrocaloric Ceramics

Lead magnesium niobate Pb(Mg_1/3Nb_2/3)O₃ — lead titanate PbTiO₃ [abbr. as (1 — x) PMN — x PT] ferroelectric ceramics with different excesses of MgO and PbO were systematically studied under different processing conditions for ferroelectric refrigeration application. It was found that the excess amount of MgO and PbO, and the sintering temperature have great effect on the crystallographic properties of the ceramics. In our experiments, (1 — x) PMN —x PT (x = 0.08, x = 0.10, and x = 0.25 respectively) with the excesses of 2 mol% MgO and 2 mol% PbO ceramics sintered at 1250 °C/1 hour possess the desired perovskite structures and large electrocaloric temperature change (ΔT = 1 K and more) in the vicinity of room temperature under a dc electric field of 1.5 kV/mm. It is expected that (1 — x) PMN — x PT electrocaloric ceramics could be applied for cascade refrigeration near room temperature.     

Structural analysis of bis{(N,N′–dimethylformamide) (μ‐formato)[μ‐bis(salicylidene)–1,3‐propanediaminato] nickel(II)} copper(II) and zinc(II) monohydrate hetero‐trinuclear complexes

The two linear hetero‐trinuclear metallic complexes with Cu²⁺, Ni²⁺ and Zn²⁺ ions, [CuNi₂ {(CHO₂)(SALPD)[(CH₃)₂NCHO]}₂],(I) and [ZnNi₂{(CHO₂)(SALPD)[(CH₃)₂NCHO]}₂],(II), form crystals which belong to the monoclinic system, space group P2₁/c, with unit cell dimensions a=10.537(4), b=16.612(5), c=13.837(3) Å, β=111.09(5)°, V=2259.8(12) ų in (I) and a=10.525(4), b=16.658(5), c=13.826(3) Å, β=111.11(5) °, V=2261.4(8) ų in (II), respectively. The coordinations around the M (Ni²⁺, Cu²⁺, Zn²⁺) ions in the title complexes are distorted octahedrals. The stereochemistries of the bridge ligands, linking to the metal ions each other, are changed between Ni…M (Cu²⁺, Zn²⁺) distances. The Ni…M (Cu²⁺, Zn²⁺) distances are 3.0469(13) and 3.0645(14), respectively. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effective electro‐optic coefficient of (1–x)Pb(Zn1/3Nb2/3)O3–xPbTiO3 single crystals

Refractive indices and effective electro‐optic coefficient γ_c of (1–x)Pb(Zn_1/3Nb_2/3)O₃–xPbTiO₃ (PZN‐xPT, x = 0.05, 0.09 and 0.12) single crystals were measured at 532 nm wavelength. Orientation and temperature dependences of the electro‐optic coefficient were investigated. Large electro‐optic coefficient (γ_c = 470 pm/V) was observed in [001]‐poled PZN‐0.09PT crystal. More importantly, γ_c of tetragonal PZN‐0.12PT is almost unchanged in a temperature range −20 ∼ 80 °C. The γ_c of PZN‐xPT single crystals are much higher than that of widely used electro‐optic crystal LiNbO₃ (γ_c = 20 pm/V). These results show that PZN‐xPT single crystals are very promising materials for electro‐optic modulators in optical communications.     

The Particularities of Infinite‐Layer Compounds Sr1–xLnxCuO2–δ (Ln=La,Pr, Nd,Eu)

The superconducting phases with general formula Sr_1–xLn_xCuO_2–δ with Ln=La (Tc=24…40K); Pr (Tc=30…44 K); Nd (Tc=8K…40 K); Eu (Tc…40 K) and non‐superconducting phases of CaCuO₂– type structure were prepared by high‐pressure synthesis. The products were examined by X‐ray powder diffraction. For the determination of composition Rietveld method was used. Structure investigations have shown that non‐superconducting phases have oxygen vacancies. With in the Cu formal charge range from 1.81 to 1.93 the infinite layer cuprates exhibit superconductivity. Coexistence of both superconducting and non‐superconducting phases of the CaCuO₂–type structure in samples with Ln=Nd and Eu was found.