Absence of Colossal Magnetoresistance in the Oxypnictide PrMnAsO0.95F0.05

ACKNOWLEDGMENTS This research is supported by the EPSRC (Research Grant EP/ L002493/1). We also acknowledge STFC-GB for provision of beamtime at ILL and ESRF.Peer reviewedPublisher PD

The Electronic and Magnetic Properties of Cation Ordered Sr2Mn2.23Cr0.77As2O2

ACKNOWLEDGMENT This research is supported by the EPSRC (research grant EP/L002493/1). We also acknowledge the UK Science and Technology Facilities Council (STFC) for provision of beam time at the ILL.Peer reviewedPostprin

The Relationship between the Crystal Structure and Electrical Properties of Oxide Ion Conducting Ba3W1.2Nb0.8O8.6

This research was supported by the University of Aberdeen and EPSRC (research grant EP/L002493/1). We also acknowledge the UK Science and Technology Facilities Council (STFC) for provision of beamtime at ISIS and the ILL.Peer reviewedPostprintPostprin

Oxide Ion Conductivity in the Hexagonal Perovskite Derivative Ba3MoNbO8.5

This research was supported by the Northern Research Partnership and the University of Aberdeen. We also acknowledge STFC-GB for provision of beamtime at ISIS.Peer reviewedPostprin

The Crystal Structure of Ba3Nb2O8 Revisited : A Neutron Diffraction and Solid-State NMR Study

JMSS, ACM and EJW acknowledge support from the University of Aberdeen for funding and RCUK/ISIS for neutron time. JVH acknowledges the continued funding of the Solid State NMR Facility and other instrumentation at Warwick used in this research which was facilitated by EPSRC, the University of Warwick and partial funding through Birmingham Science City Advanced Materials Projects 1 and 2, which in turn was supported by Advantage West Midlands (AWM) and the European Regional Development Fund (ERDF).Peer reviewedPostprin

High oxide ion and proton conductivity in a disordered hexagonal perovskite

This research was supported by the Leverhulme trust and EPSRC (MISE). We also acknowledge STFC-GB for provision of beamtime at the ILL.Peer reviewedPostprintPostprin

Colossal Magnetoresistance in the Mn2+ Oxypnictides NdMnAsO1-xFx

Colossal magnetoresistance (CMR) is a rare phenomenon in which the electronic resistivity of a material can be decreased by orders of magnitude upon application of a magnetic field. Such an effect could be the basis of the next generation of magnetic memory devices. Here we report CMR in the antiferromagnetic oxypnictide NdMnAsO1-xFx as a result of competition between an antiferromagnetic insulating phase with strong electron correlations and a paramagnetic semiconductor upon application of a magnetic field. The discovery of CMR in antiferromagnetic Mn2+ oxypnictide materials could open up an array of materials for further investigation and optimisation for technological applications

The Electrical and Structural Characterization of Ba3Mo1-xNb1+xO8.5-x/2 : The relationship between mixed coordination, polyhedral distortion and the ionic conductivity of Ba3MoNbO8.5

This research was supported by the Northern Research Partnership and the University of Aberdeen. We also acknowledge STFC-GB for provision of beamtime at the ILL.Peer reviewedPostprintPostprin

Enhanced Oxide Ion Conductivity by Ta Doping of Ba₃Nb_1<i>–x</i>Ta_<i>x</i>MoO_8.5

Significant oxide ion conductivity has previously been reported for the Ba3M′M″O8.5 family (M′ = Nb5+, V5+; M″ = Mo6+, W6+) of cation-deficient hexagonal perovskite derivatives. These systems exhibit considerable structural disorder and competitive occupation of two distinct oxygen positions (O3 site and O2 site), enabling two-dimensional (2D) ionic conductivity within the ab plane of the structure; higher occupation of the tetrahedral O3 site vs the octahedral O2 site is known to be a major factor that promotes oxide ion conductivity. Previous chemical doping studies have shown that substitution of small amounts of the M′ or M″ ions can result in significant changes to both the structure and ionic conductivity. Here, we report on the electrical and structural properties of the Ba3Nb1–xTaxMoO8.5 series (x = 0.00, 0.025, 0.050, 0.100). AC impedance measurements show that substitution of Nb5+ with Ta5+ leads to a significant increase in low-temperature (x = 0.1. Analysis of neutron and X-ray diffraction (XRD) data confirms that there is a decrease in the M1O4/M1O6 ratio upon increasing x from 0 to 0.1 in Ba3Nb1–xTaxMoO8.5, which would usually coincide with a lowering in the conductivity. However, neutron diffraction results show that Ta doping causes an increase in the oxide ion conductivity as a result of longer M1–O3 bonds and increased polyhedral distortion