Carbonate : an alternative dopant to stabilize new perovskite phases ; synthesis and structure of Ba3Yb2O5CO3 and related isostructural phases Ba3Ln2O5CO3 (Ln = Y, Dy, Ho, Er, Tm and Lu)

In this paper we report the synthesis of the new layered perovskite oxide carbonate, Ba3Yb2O5CO3. This phase is formed when 3BaCO(3):1Yb(2)O(3) mixtures are heated in air at temperatures 1000 degrees C, while above this temperature the carbonate is lost and the simple oxide phase Ba3Yb4O9 is observed. The structure of Ba3Yb2O5CO3 was determined from neutron diffraction studies and consists of a tripled perovskite with double Yb-O layers separated by carbonate layers, the first example of a material with such a structure. Further studies showed that analogous Ba(3)Ln(2)O(5)CO(3) phases could be formed for other rare earths (Ln = Y, Dy, Ho, Er, Tm and Lu). The results highlight the ability of the perovskite structure to accommodate carbonate groups, and emphasise the need to consider their potential presence particularly for perovskite systems prepared in lower temperature synthesis routes

Understanding the complex structural features and phase changes in Na2Mg2(SO4)3:a combined single crystal and variable temperature powder diffraction and Raman spectroscopy study

Sodium mixed metal sulphates have attracted considerable attention, both in terms of mineralogy and more recently due to interest in Na ion containing materials for battery applications. The phase, Na 2 Mg 2 (SO 4 ) 3 , has been previously reported to undergo a phase change to langbeinite at high temperatures, which is interesting given that usually the langbeinite structure is only adopted when large alkali metal ions, e.g. K, Cs, are present. Nevertheless the room temperature structure of this phase has remained elusive, and so in this work, we report a detailed structural study of this system. We show that room temperature Na 2 Mg 2 (SO 4 ) 3 can only be prepared by quenching from high temperature, with slow cooling leading to phase separation to give the previously unreported systems, Na 2 Mg(SO 4 ) 2 and Na 2 Mg 3 (SO 4 ) 4 . We report the structures of quenched Na 2 Mg 2 (SO 4 ) 3 (monoclinic, P2 1 ), as well as Na 2 Mg(SO 4 ) 2 (triclinic, P1¯) and Na 2 Mg 3 (SO 4 ) 4 (orthorhombic, Pbca), detailing their complex structural features. Furthermore, we report a study of the thermal evolution of quenched Na 2 Mg 2 (SO 4 ) 3 with temperature through variable temperature XRD and Raman studies, which shows a complex series of phase transitions, highlighting why this phase has proven so elusive to characterise previously, and illustrating the need for detailed characterisation of such sulphate systems

Mechanism of carbon dioxide and water incorporation in Ba2TiO4: A joint computational and experimental study

© 2017 American Chemical Society. CO 2 incorporation in solids is attracting considerable interest in a range of energy-related areas. Materials degradation through CO 2 incorporation is also a critical problem with some fuel cell materials, particularly for proton conducting ceramic fuel cells. Despite this importance, the fundamental understanding of the mechanism of CO 2 incorporation is lacking. Furthermore, the growing use of lower temperature sol gel routes for the design and synthesis of new functional materials may be unwittingly introducing significant residual carbonate and hydroxyl ions into the material, and so studies such as the one reported here investigating the incorporation of carbonate and hydroxyl ions are important, to help explain how this may affect the structure and properties. This study on Ba 2 TiO 4 suggests highly unfavorable intrinsic defect formation energies but comparatively low H 2 O and CO 2 incorporation energies, in accord with experimental findings. Carbonate defects are likely to form in both pristine and undoped Ba 2 TiO 4 systems, whereas those based on H 2 O will only form in systems containing other supporting defects, such as oxygen interstitials or vacancies. However, both hydroxyl and carbonate defects will trap oxide ion defects induced through doping, and the results from both experimental and modeling studies suggest that it is primarily the presence of carbonate that is responsible for stabilizing the high temperature α′-phase at lower temperatures

Investigation of structure and properties of Li/Na ion conducting electrolytes and electrode materials

This thesis describes the synthesis, structure and properties of a range of materials to be used in Li/Na ion batteries. As potential solid electrolytes, Si/B doped lithium lanthanum titanium oxide (LLTO) perovskites, Na doped Nb/Ta/Zr-based garnets and mixed Na/K-Mg sulphates were studied. The oxoanion doped eldfellite material and mixed Na/K-Ti/V phosphates were studied as potential cathode materials. The silicon and boron doped LLTO perovskites were shown to have better sinterability but have a lower ionic conductivity. Na doped garnets demonstrated the ability to incorporate Na onto the La site with partial incorporation to the Li site as well, therefore blocking Li transport. New systems were reported for Na-Mg sulphates. The detailed X-ray diffraction study of $Na_2Mg_2(SO_4)_3$ highlights enormous complexities within the system. The thermal evolution of these phases was studied. The eldfellite $NaFe(SO_4)_2$ was demonstrated to be able to have 25% of sulphate replaced with hydrophosphate and selenate anions without degrading the structure. Mixed Na/K-Ti/V phosphates were shown to form two different structures: NASICON and langbeinite with unusual cell parameter changes

ON ELECTROCHEMICAL ACTIVITY OF ZN2(EDTA)(H2O) IN AQUEOUS SODIUM-ION BASED ELECTROLYTES

Metal-organic frameworks (MOFs) are a class of compounds consisting of metal ions or clusters coordinated to organic ligands to form one-, two-, or three-dimensional structures. Due to their high porosity and excellent adsorption and catalytic activity, as well as the ability to simultaneously implement different charge accumulation mechanisms (ions de/intercalation and adsorption/desorption), they can be considered as electrode materials for metal-ion batteries. However, a significant drawback is that most MOFs have low conductivity, and the obtaining of conducting MOFs is a costly, time-consuming and technically difficult process

POLYCATIONIC DOPING OF THE LATP CERAMIC ELECTROLYTE FOR LI-ION BATTERIES

All-solid-state Li-ion batteries (LIBs) with a solid electrolyte instead of a liquid one demonstrate significantly higher safety in contrast with the conventional liquid-based LIBs. An inorganic NASICON-type Li conductor Li1.3Al0.3Ti1.7(PO4)3 (LATP) is a promising solid electrolyte with an ionic conductivity of up to 10−3 S cm−1 at room temperature. However, LATP gradually degrades in contact with Li metal because of reduction of Ti4+ to Ti3+, resulting in a lower ionic conductivity at the electrolyte–electrode interface. Cation doping is a promising approach to stabilize the LATP structure and mitigate the Ti reduction. Here, we report our findings on the alternative polycationic doping strategy of the LiTi2(PO4)3 (LTP) structure, when a heterovalent cation is added along with Al. In particular, we studied the effect of tetravalent and divalent cation dopants (Zr, Hf, Ca, Mg, Sr) of LATP on the Li-ion conduction and Ti reduction during interaction with lithium metal. The samples were prepared by molten flux and solid-state reaction methods. The structure, morphology, and ion-transport properties of the samples were analyzed. The activation energy of Li-ion migration in all synthesized systems was calculated based on the electrochemical impedance spectroscopy (EIS) data retrieved for a temperature range of 25–100 °C. From the obtained results, the tetravalent doping (Zr4+ and Hf4+) appeared to be a more promissing route to improve the LATP electrolyte than the divalent doping (Mg2+, Ca2+, and Sr2+). The X-ray photoelectron spectroscopy analysis of the samples after their contact with lithium provided the data, which could shed light on the effect of the incorporated dopants onto the Ti reduction

Mechanism of Carbon Dioxide and Water Incorporation in Ba₂TiO₄:A Joint Computational and Experimental Study

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.jpcc.7b10330© 2017 American Chemical Society. CO 2 incorporation in solids is attracting considerable interest in a range of energy-related areas. Materials degradation through CO 2 incorporation is also a critical problem with some fuel cell materials, particularly for proton conducting ceramic fuel cells. Despite this importance, the fundamental understanding of the mechanism of CO 2 incorporation is lacking. Furthermore, the growing use of lower temperature sol gel routes for the design and synthesis of new functional materials may be unwittingly introducing significant residual carbonate and hydroxyl ions into the material, and so studies such as the one reported here investigating the incorporation of carbonate and hydroxyl ions are important, to help explain how this may affect the structure and properties. This study on Ba 2 TiO 4 suggests highly unfavorable intrinsic defect formation energies but comparatively low H 2 O and CO 2 incorporation energies, in accord with experimental findings. Carbonate defects are likely to form in both pristine and undoped Ba 2 TiO 4 systems, whereas those based on H 2 O will only form in systems containing other supporting defects, such as oxygen interstitials or vacancies. However, both hydroxyl and carbonate defects will trap oxide ion defects induced through doping, and the results from both experimental and modeling studies suggest that it is primarily the presence of carbonate that is responsible for stabilizing the high temperature α′-phase at lower temperatures