We address the controversial issue of the structural stability of Li 7 La 3 Zr 2 O 12 garnets, focusing on the mechanisms that result in the transformation from tetragonal to cubic symmetry. We show that undoped tetragonal Li 7 La 3 Zr 2 O 12 not exposed to humidity at any moment undergoes a reversible phase transition to cubic symmetry at T c x 645 C that we ascribe to lithium dynamic effects. On the other hand, a close correlation has been found between the appearance of a cubic phase between 100 and 200 C in X-ray diffractograms and the presence of water, either in the atmosphere in which experiments are performed or already in the starting material. The natures of the high and lowtemperature cubic garnets are totally different: the one found above the phase transition does not involve any change in the stoichiometry, whereas the cubic phase formed at low temperature is a hydrated, lithium defective phase, due to the combined effect of water insertion into the garnet structure and the H + /Li + exchange mechanism. Differences in the actual compositions of the samples depending on their thermal history are corroborated by TG-MS experiments. Chemical reactions and phases formed along the thermal evolution are elucidated with the help of Raman spectroscopy.

No abstract

With appropriate doping or processing, Li7La3Zr2O12 (LLZO) is an excellent candidate to be used in Li batteries either as a solid electrolyte or as a separator between the Li anode and a liquid electrolyte. For both uses, the reactivity with water either from the air or in aqueous media is a matter of interest. We address here the structural changes undergone by LLZO as a result of H(+)/Li(+) exchange and relate them with the amount of H content and atomic distribution. Neutron diffraction is performed to elucidate Li and H location. Two different cubic phases derive from LLZO through H(+)/Li(+) exchange: Deep hydration up to 150 °C yields a noncentrosymmetric I4̅3d phase in which octahedral Li ions are exchanged by H ions, tetrahedral Li ions split into two sites with very different occupancies, and H ions form O4H4 entities around the less occupied tetrahedral site. Annealing above 300 °C results in a centrosymmetric Ia3̅d phase with lower H content in which Li ions occupy the usual sites of the cubic garnets and H ions occupy a split pseudooctahedral site. The centrosymmetric or noncentrosymmetric character is determined by the temperature at which exchange is performed and the H content. Both factors are not independent: at low temperature, the high H content favors H ordering around the vacant tetrahedra, while low H content and higher mobility at 350 °C lead to a disordered configuration of Li and H ions. The deeply hydrated garnets are stable up to at least 300 °C and also upon aging at room temperature.

No abstract

During 2004, a survey of Mycobacterium avium subspecies paratuberculosis (map) was conducted in 101 randomly selected dairy herds to investigate associations between the infection status of the herds, different management practices, and possible disease indicators, such as indices of mastitis and reproductive performance. Data were collected by means of a questionnaire through personal interviews with the farmers and veterinarians in charge of each farm. At the same time, blood samples were taken from cattle over one year old and analysed with a commercial elisa to detect antibodies to map. Statistical analyses indicated that the following management practices constituted major risk factors: utilisation of colostrum from cows with a previous positive map diagnosis, and housing replacement calves with adult cattle before they were six months old. Seropositivity to map was related to the herds' bulk tank somatic cell counts and incidence of clinical mastitis, but not to their reproductive performance.

We present a NMR investigation of 6Li7−xHxLa3Zr2O12 (0 ≤ x ≤ 5) garnets to study the distribution of Li ions. The facile H+/Li+ exchange alters the relative population of Li sites, and allows the identification of 3 different bands ascribed to Li in different environments. Variable temperature measurements indicated the presence of dynamic processes between octahedral and tetrahedral Li sites.

No abstract

No abstract