Dipolar relaxation and the impedance of yttria-stabilised zirconia ceramic electrolyte

Equivalent circuit analysis of ac impedance data for yttria-stabilised zirconia ceramics shows evidence for dipole relaxation at intermediate frequencies in addition to the long range, oxide ion conduction. Dipoles, or larger clusters, arise from the association between substitutional Y3+ ions and oxide ion vacancies. Resistance values for dipole relaxation have similar activation energies to those associated with long range conduction through both bulk and grain boundaries, of approximately 1.1 eV, since both processes involve oxide ion migration

On the correct choice of equivalent circuit for fitting bulk impedance data of ionic/electronic conductors

Bulk conductivity data of ionically and electronically conducting solid electrolytes and electronic ceramics invariably show a frequency dependence that cannot be modelled by a single-valued resistor. To model this, common practice is to add a constant phase element (CPE) in parallel with the bulk resistance. To fit experimental data on a wide variety of materials, however, it is also essential to include the limiting, high frequency permittivity of the material in the equivalent circuit. Failure to do so can lead to incorrect values for the sample resistance and CPE parameters and to an inappropriate circuit for materials that are electrically heterogeneous

Pesticides on millet in Mali (NRI Bulletin 50)

The Mali Millet Pest Project (Projet Pilote Britannique), financed by Britain's Overseas Development Administration (ODA) studied the control of millet pests in north-west Mali between 1985 and 1991. The project was executed by Mali's Service National de Protection des vegetaux (SNPV) and ODA's Natural Resources Institute (NRI). These six years of observations, field trials and socio-economic research have produced a wealth of information on the pests of Sahelian millet

Phase formation, crystallography and ionic conductivity of lithium manganese orthosilicates

On the orthosilicate join, Li4SiO4–Mn2SiO4, the new phase Li3Mn0.5SiO4 and a range of Li2+2xMn1–xSiO4 solid solutions with ∼0.76 ≤ x ≤ 1 have been prepared by high-temperature, solid-state reaction and characterized. Li3Mn0.5SiO4 is orthorhombic, space group Pnma, with a = 10.722(3) Å, b = 6.239(2) Å, and c = 5.052(3) Å. A combined analysis of X-ray and neutron powder diffraction data show that its structure is derived from the γII tetrahedral structural family typified by Li3PO4, but with additional Li+ in partially occupied, distorted octahedral sites. These octahedral sites are linked by a combination of edge- and face-sharing, similar to that in the nickel arsenide structure and their partial occupancy is responsible for an Li+ ion conductivity of, for example, ∼ 1 × 10–8 S cm–1 at 60 °C, with activation energy 0.93(1) eV, which is many orders of magnitude higher than that of Li2MnSiO4

Incidence and repetition of deliberate self-harm in three remote Indigenous communities in Far North Queensland, Australia

Aim: To investigate the incidence and repetition of deliberate self-harm (DSH) using data from a clinical file audit for the period 2006-2011 in three remote Indigenous communities in Far North Queensland. Background: Deliberate self-harm (DSH) is a global public health concern. It is the single most important risk factor for suicide (Cooper, et al., 2005) with a higher frequency over time associated with a greater acquired ability for suicide (Willoughby, et al., 2015). Therefore, understanding the incidence and repetition of DSH is crucial for services and practitioners concerned with the prevention of suicidal behavior (Perry, et al., 2012). Method: The study communities are located on the Cape York Peninsula in Far North Queensland, Australia. These communities are very remote, experience a similarly low sociodemographic ranking, and the great majority of the population are Indigenous Australians. A clinical file audit was performed at the primary health clinic in each community for the six year period from 1st January 2006 to 31st December 2011. Presentations involving DSH were extracted and analysed to characterise the incidence and repetition of DSH in these communities

Redox-active oxygen in oxides: emergent applications, including field-induced resistive switching, flash luminescence, p–n junctions and high capacity battery cathodes

Oxide ions are traditionally regarded as forming the inert anion sub-lattice of oxide structures whose properties are largely dominated by the cations present. This viewpoint is being increasingly challenged by examples of a diverse range of phenomena in which some of the oxide ions present are redox-active. The source of this activity in ionic structures is the inherent instability of O2− ions in the gas phase which are stabilised in crystal lattices by the additional lattice energy associated with doubly-charged anions. Oxide ions located either at sample surfaces or adjacent to lower valence (acceptor) substitutional cations, may not be fully stabilised, as they are surrounded by an effective positive charge of less than 2+. They are under-bonded and may ionise, either spontaneously or with reduced ionisation potential. Examples of oxygen redox include: high capacity Li and Na battery cathodes in which there is insufficient redox-active transition metal component present to account for the observed charge/discharge capacities; electroceramic materials such as some doped titanate perovskites which exhibit hopping p-type conductivity and in which the only realistic location of the electron holes is on lattice oxide ions; novel resistive switching phenomena and insulator-metal transitions in oxide ceramics; resistance degradation of insulating ceramics prior to dielectric breakdown; flash luminescence by creation of p–n junctions in oxide ceramics; possible origin of 2-dimensional electron gases in layered superlattices formed from oxide insulators. The underlying principles of oxygen redox activity are set out and its possible contribution to emergent phenomena are discussed

Investigation of Antisite Defect Formation and Chemical Expansion in LiNiPO4 by in Situ Neutron Diffraction

In situ neutron diffraction was used to characterize the effect of temperature on the crystal structure of LiNiPO4. LiNiPO4 adopts an ordered olivine structure at room temperature, but, with increasing temperature, this work shows that a significant amount of Li and Ni cation exchange occurs, for example, ∼15% at 900 °C. The antisite disorder is detected by residual nuclear densities on the M1 and M2 octahedral sites in the olivine structure using difference Fourier maps and by changes in cation site occupancies, lattice parameters, and mean ⟨M–O⟩ bond distances. The antisite disorder is also responsible for chemical expansion of the crystal lattice in addition to thermal expansion. Antisite defect formation at high temperature and its reversibility on cooling can be understood as an entropically driven feature of the crystal structure of LiNiPO4. The lithium ion diffusion pathway, that follows a curved trajectory along the b axis in the olivine structure, is, therefore, susceptible to be blocked if synthesis conditions are not carefully controlled and should also be influenced by the chemically expanded lattice of the disordered structure if this is preserved to ambient temperature by rapid cooling

Induced p‐type semi‐conductivity in yttria‐stabilised zirconia

8 mol% yttria‐stabilized zirconia (8YSZ) ceramic is an oxide ion conductor at atmospheric pressure but shows the onset of p‐type semiconduction, in addition to the preexisting oxide ion conduction, on application of a dc bias in the range 4‐66 Vcm−1 and at temperatures in the range 150°C‐750°C. The p‐type behavior is attributed to the location and hopping of holes on oxygen. This contrasts with the commonly observed introduction of n‐type conduction under reducing conditions and high fields. The hole conductivity increases with both dc bias and pO2. Its occurrence may contribute to the early stages of flash phenomena in 8YSZ ceramics

Electrical properties of yttria-stabilized zirconia, YSZ single crystal: Local AC and long range DC conduction

Widely-used complex plane analysis of impedance data is insufficiently sensitive to characterize fully the bulk properties of YSZ single crystal. Instead, more extensive data analysis is needed which uses a combination of parallel, admittance-based formalisms and series, impedance-based formalisms. Bulk electrical properties are measured at higher frequencies and contain contributions from both long range conduction and local dielectric relaxation. At lower frequencies, electrode–sample contact impedances are measured and are included in full equivalent circuit analysis. The impedance of YSZ crystal of composition 8 mol% Y2O3 in the (110) orientation, with Pt electrodes, was measured over the temperature range 150–750°C and frequency range 0.01 Hz-3 MHz. Full data analysis required (i) a parallel constant phase element (CPE)–resistance (R) combination to model the electrode response, (ii) a series R-C element to represent local reorientation of defect dipoles and (iii) a R-C-CPE element to represent long range oxide-ion conduction; (ii) and (iii) together model the bulk response. The dielectric element underpins all discussions about defect structure and properties of YSZ but has not been included previously in analysis of impedance data. The new equivalent circuit that is proposed should allow better separation of bulk and grain boundary impedances of YSZ ceramics

Electrical properties of calcia-stabilised zirconia ceramics

The electrical properties of cubic, calcia-stabilised zirconia ceramics, CaxZr1-xO2-x: 0.12 ≤ x ≤ 0.18 have been investigated using impedance spectroscopy to separate bulk, grain boundary and electrode contact impedances. The most appropriate equivalent circuit to characterise the bulk response required inclusion of a dielectric component, represented by a series RC element, in parallel with the oxide ion conductivity represented by a parallel combination of a resistance, capacitance and constant phase element. The dielectric component may be attributed to defect complexes involving immobile oxygen vacancy pairs whereas long range conduction involves single oxygen vacancies