No. Barn0393 Pressure-Induced Cation Migration and Volume Expansion in Defect Pyrochlore Oxides P. W. Barnes (Ohio State Univ., Chemistry), P. M. Woodward (Ohio State Univ., Chemistry), Y. Lee (BNL, Physics), T. Vogt (BNL, Physics), J. A. Hriljac (Univ. Birmingham, Chemical Sciences) Beamline(s): X7A Introduction: Microporous materials, such as zeolites [1,2], undergo pressure-induced volume ex...

– The Ising-like spin ice model, with a macroscopically degenerate ground state, has been shown to be approximated by several real materials. Here we investigate a model related to spin ice, in which the Ising spins are replaced by classical Heisenberg spins. These populate a cubic pyrochlore lattice and are coupled to nearest neighbours by a ferromagnetic exchange term J and to the local 〈1, 1...

We argue that the analysis of Reimers et al. (1992)] of their Monte Carlo data on the Heisenberg pyrochlore antiferromag-net, which suggests a new universality class, is not conclusive. By re-analysis of their data, we demonstrate asymptotic volume dependence in some ther-modynamic quantities, which suggests the possibility that the transition may be first order.

A combination of (89)Y and (119)Sn NMR spectroscopy and DFT calculations are used to investigate phase evolution, local structure and disorder in Y2Zr2-xSnxO7 ceramics, where a phase change is predicted, from pyrochlore to defect fluorite, with increasing Zr content. The ability of NMR to effectively probe materials that exhibit positional and compositional disorder provides insight into the at...

Since the beginning of use nuclear energy, humans have been faced with problem radionuclide disposal. At present, a large amount waste is stored in pools or dry tanks at reactor sites. With development power generation industry worldwide, high storage cost (including building, maintaining, and operating pools) overwhelming serious, urgent disposal problems become increasingly difficult. Safe ec...

A series of zirconolite ceramics with composition CaZr1‐xThxTi2O7 (Δx = 0.10) were reactively sintered at 1350 ˚C for 20 h, in air (0 ≤ x 0.60) and 5% H2/N2 0.40). sample corresponding to 0.20 was also produced by hot isostatic pressing (HIP) 1300 100 MPa 4 h. Th4+ immobilisation most readily achieved under oxidising conditions, preferentially incorporated within a pyrochlore‐structured phase t...

The design of new oxygen- and proton-conducting materials is paramount importance for their possible utilization in solid oxide fuel cells. In the present work, La2(Hf2–xLax)O7–x/2 (x = 0, 0.1) ceramics were prepared using ball milling mixtures (La2O3 HfO2) followed by high-temperature annealing at 1600 °C 10 h air. La2Hf2O7 exhibit an ordered pyrochlore-type structure, whereas La2(Hf1.9La0.1)O...

Abstract. We present a detailed symmetry analysis of the degeneracy lifting due to higher order spin exchanges in the pyrochlore lattice in applied magnetic field. Under the assumption of the 4 sublattice ordering, the criteria for a stable half-magnetization plateau are deduced. The higher order exchange terms may originate from spin–lattice coupling, or can describe quantum and thermal fluctu...

We show that a continuous set of degenerate critical soft modes strongly enhances the first-order character of a fluctuation-induced first-order transition in the pyrochlore dipolar Heisenberg antiferromagnet. Such a degeneracy seems essential to explain the strong first-order transition recently observed in Gd2Sn2O7. We present some evidence from Monte Carlo simulations and a perturbative reno...