The Main Belt Comets and ice in the Solar System

We review the evidence for buried ice in the asteroid belt; specifically the questions around the so-called Main Belt Comets (MBCs). We summarise the evidence for water throughout the Solar System, and describe the various methods for detecting it, including remote sensing from ultraviolet to radio wavelengths. We review progress in the first decade of study of MBCs, including observations, modelling of ice survival, and discussion on their origins. We then look at which methods will likely be most effective for further progress, including the key challenge of direct detection of (escaping) water in these bodies

Defect structure of the mixed ionic–electronic conducting Sr[Ti,Fe]Ox solid-solution system — Change in iron oxidation states and defect complexation

The oxidation/reduction behavior of iron in the Sr[Ti1 − yFey]Ox solid-solution system, for y set membership, variant [0.002; 0.05], under various oxygen partial pressures was examined through the use of electron paramagnetic resonance (EPR) spectroscopy. The results indicate that iron has been induced to move between di- tri- and tetravalent oxidation states. This results with the centers functioning as either a source (oxidation) or as a sink (reduction) for electrons. In particular it is shown that the reducibility of iron decreases with increasing iron content

Defect structure and formation of defect complexes in Cu2+-modified metal oxides derived from a spin-Hamiltonian parameter analysis

The nearest neighbour oxygen octahedron about copper functional centres in metal oxides has been systematically studied by means of electron paramagnetic resonance (EPR) spectroscopy. In particular, the determined g||zz and ACu||zz spin-Hamiltonian parameters were analysed, finding linear dependences as a function of chemical bonding and local distortion of the oxygen octahedron. Moreover, through the introduction of a dimensionless coordination parameter ξ, different defect structures with respect to the number of coordinated oxygen vacancies may be distinguished. This allows for a distinct assignment of defect complexes between the copper functional centre with one or two oxygen vacancies

Local variations in defect polarization and covalent bonding in ferroelectric Cu2+-doped PZT and KNN functional ceramics at the morphotropic phase boundary

Cu2+-doped Pb[Zr0.54Ti0.46]O3 (PZT) and Cu2+-doped [K0.5Na0.5]NbO3 (KNN) ferroelectrics with a dopant concentration of 0.25 mol% were investigated by means of multi-frequency and multi-pulse electron paramagnetic resonance (EPR) spectroscopy. Through the use of high magnetic fields and pulsed microwave fields an enhanced resolution was achieved yielding valuable information about the structural distortion at the dopant site. The results obtained suggest that Cu2+ substitutes for both systems as an acceptor centre for the perovskite B-site. For reasons of local charge compensation, different kinds of defect associates invoking one and two oxygen vacancies are formed. These two kinds of extended defects differ in their electric and elastic properties. The results obtained are analyzed in order to characterize differences of the local structure in the Cu2+-defect center for morphotropic phase boundary compositions between the two systems. In particular, it is found that Cu2+-doping in KNN creates 50% more oxygen vacancies than the same amount of copper in PZT. Furthermore, local differences in covalent and ionic bonding are monitored

DEFECT STRUCTURE IN "SOFT" (Gd,Fe)-CODOPED PZT 52.5/47.5 PIEZOELECTRIC CERAMIC

Ferroelectric 1 mol% Gd3+ and 0.5 mol% Fe3+ codoped "soft" Pb[Zr0.525Ti0.475]O3 ceramics were studied by means of multifrequency electron paramagnetic resonance (EPR) spectroscopy. The obtained results prove that iron is incorporated at the [Zr,Ti]-site, acting as an acceptor and building a charged (Fe'Zr,Ti - Vo°°)° defect dipole with a directly coordinated oxygen vacancy for partial charge compensation. As the La3+ ion is diamagnetic, no information is accessible about the donor. Gd3+ is an isoelectronic and paramagnetic probe for studying A-site. On the other hand, the donor forms no defect associates with lattice vacancies and rather exists as an "isolated" functional center. Consequently, also the lead vacancies that are created for charge compensation have to exist as isolated centers in compound

Manganese-doped (1−x)BiScO_{3}–xPbTiO_{3} high-temperature ferroelectrics: Defect structure and mechanism of enhanced electric resistivity

The effect of multivalency manganese doping on the defect structure and enhanced electrical resistivity is studied for the high-temperature piezoelectric (1−x)BiScO3–xPbTiO3 (BSPT) solid-solution system by means of multifrequency electron paramagnetic resonance spectroscopy combined with conductivity measurements. The results show that manganese is rather incorporated on a scandium than a titanium site as an isovalent substitute (MnSc×) instead of acceptor-type centers, such as MnTi′, MnTi′′, or MnSc′. The enhanced electric resistivity is found being on the one hand due to the trapping of conduction electrons at the manganese functional center sites (MnSc×+e′MnSc′). On the other hand, through the formation of (MnSc′−VO••)• defect complexes the ionic conductivity is reduced. Concerning the overall mechanism of charge compensation in that material, both kinds of defects mutually compensate