Negative thermal expansion (NTE) of BiNi 1Àx Fe x O 3 is investigated. All x ¼ 0.05, 0.075, 0.10, and 0.15 samples shows large NTE with the coefficient of linear thermal expansion (CTE) a L exceeding À150 ppm K À1 induced by charge transfer between Bi 5þ and Ni 2þ in the controlled temperature range near room temperature. Compared with Bi 1Àx Ln x NiO 3 (Ln: rare-earth elements), the thermal hysteresis that causes a problem for practical application is suppressed because random distribution of Fe in the Ni site changes the first order transition to second order-like transition. The CTE of BiNi 0.85 Fe 0.15 O 3 reaches À187 ppm K À1 and it is demonstrated that 18 vol. % addition of the present compound compensates for the thermal expansion of epoxy resin. V C 2015 AIP Publishing LLC. [http://dx.
A new PbTiO 3 -type compound, Bi 2 ZnVO 6 , with a giant tetragonal distortion of c/a = 1.26 (a = 3.7869(3) Å, c = 4.7660(7) Å) was synthesized under high pressure−high temperature conditions (9 GPa and 1373 K). A point charge model calculation based on the atomic positions refined by Rietveld analysis of synchrotron X-ray diffraction (SXRD) data gave an electrical ionic polarization of 126 μC/cm 2 , the largest value among PbTiO 3 -type perovskite compounds. The tetragonality (c/a) decreased with increasing temperature from 100 to 570 K without any trace of a phase transition. Instead, a pressure-induced transition from a polar tetragonal structure to a paraelectric GdFeO 3 one accompanied by a 2.4% volume collapse was observed at 6.01 GPa. Bi 2 ZnVO 6 showed paramagnetic behavior with S = 1/2 because of the random distribution of nonmagnetic Zn 2+ and magnetic V 4+ ions. Transport measurements indicated semiconductivity with an activation energy of 0.43 eV. ■ INTRODUCTIONPbTiO 3 is a typical ferroelectric material with a large spontaneous polarization resulting from displacement of the B-site ion of ABO 3 perovskite from the center of the octahedron leading to a pyramidal rather than octahedral coordination. This distorted structure is stabilized by the 6s 2 lone electron pair of the Pb 2+ ion and by hybridization between the Pb 6s and O 2p orbitals. 1,2 PbTiO 3 constitutes PbZr x Ti 1−x O 3 (PZT), which shows outstanding piezoelectric properties at the morphotropic phase boundary (MPB) with the PbZrO 3 -based rhombohedral phase. 3−8 Because of the growing concern about lead toxicity, the search is on for new lead-free compounds, such as PbTiO 3 -type perovskite or potassium sodium niobate (KNN)-based materials, as potential replacements for PZT. 9−19 Several PbTiO 3 -type compounds with enhanced c/a ratios, such as PbVO 3 , 9,10 BiCoO 3 , 11 Bi 2 ZnTiO 6 , 12 and BiFeO 3 in thin film form 13 have recently been found.PbVO 3 has a c/a ratio of 1.23, much larger than that of PbTiO 3 (1.06). The temperature dependence of the magnetic susceptibility measured on single crystals indicated a twodimensional antiferromagnetism originating from the ordering of d xy orbitals, which is thought to be related to the large tetragonal distortion. 20 A tetragonal to cubic phase transition under pressure accompanied by a 9.4% volume collapse and drop in electrical resistivity was observed. 9,21 BiCoO 3 has an even larger distortion, with a c/a ratio of 1.27. Neutron diffraction measurements indicated a C-type antiferromagnetic ordering of high-spin Co 3+ magnetic moments. 11 A pressureinduced phase transition accompanied by a 13% volume collapse and spin state transition was also observed. 22 A monoclinic phase with a √2a × √2a × a unit cell, where a is the lattice parameter of a cubic perovskite and Cm space group, the same as in the low temperature phase of the MPB composition of PZT, was found in a solid solution between BiCoO 3 and rhombohedral BiFeO 3 . 23,24 Bi 2 ZnTiO 6 is a B-site mixed double perovskite compound with a ...
The valence distribution and local structure of Bi 1−x Pb x NiO 3 (x ≤ 0.25) were investigated by comprehensive studies of Rietveld analysis of synchrotron X-ray diffraction (SXRD) data, X-ray absorption spectroscopy (XAS), hard X-ray photoemission spectroscopy (HAXPES), and pair distribution function (PDF) analysis of synchrotron X-ray total scattering data. Disproportionation of Bi ions into Bi 3+ and Bi 5+ was observed for all the samples, but it was a longranged one with distinct crystallographic sites in the P1̅ triclinic structure for x ≤ 0.15, while the ordering was short-ranged for x = 0.20 and 0.25. An intermetallic charge transfer between Bi 5+ and Ni 2+ , leading to large volume shrinkage, was observed for all the samples upon heating at ∼500 K.
Electrical properties of C n TCNQ Langmuir-Blodgett films sandwiched between aluminum electrodes are studied using thermally stimulated electrical measurements, and both the effect of film structure and the influence of native aluminum oxide are stressed. A change in induced charges on an electrode (Δq 2) is measured while heating a sample. The relation between Δq 2 and the number of deposited layers is in good agreement with a simple model based on a double-layered dielectric system. The direction of polarization in a film as deposited is also investigated using a photo-induced current measurement.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.