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We measure the effects of transverse wakefields driven by a relativistic proton bunch in plasma with densities of 2.1×1014 and 7.7×1014 electrons/cm3. We show that these wakefields periodically defocus the proton bunch itself, consistently with the development of the seeded self-modulation process. We show that the defocusing increases both along the bunch and along the plasma by using time resolved and time-integrated measurements of the proton bunch transverse distribution. We evaluate the transverse wakefield amplitudes and show that they exceed their seed value (

The macroscopic reproduction of the various solid-solid interfaces expected in the synthesis of BaTiO3 from BaCO3 and TiO2 enabled us to describe the reaction stages in visualizing the diffusion of the entities concerned as well as the domains undergoing transformation. The following results were established or confirmed, (a) Firstly, metatitanate BaTiO3 forms at the expense of TiO2 by diffusion of barium from BaCO3. (b) Secondly, orthotitanate Ba2TiO4 forms at the expense of the BaTiO3 layer by diffusion of barium from BaCO3. (c) Finally, the orthotitanate is converted into BaTiO3 releasing an unidentified species of BaO stoichiometry which diffuses towards TiO2 through BaTiO3 to form BaTiO3.

La diffraction des rayons-X et la thermogravimetrie ont permis d'identifier le role de l'environnement et le temps de la transformation durant la synthese du metatitanate de baryum a partir du BaCO 3 et TiO 2

Les auteurs ont recherche l'effet du broyage sur la reactivite ulterieure des hydrates K2C2O4 · H2O; CaC2O4· H2O et BaC2O4 ·nH2O avecn=0, 1/2, 1 et 2. La thermolyse de ces hydrates prealablement broyes montre que le traitement mecanique provoque dans la plupart des cas un abaissement de la temperature de deshydratation mais aussi, dans certains cas, une modification des etapes de cette reaction. Ces effets se manifestent surtout lorsque le broyage prealable est de courte duree et ils peuvent etre modifies par les conditions de pression et de temperature imposees pendant le traitement mecanique. La comparaison des variations, en fonction du temps de broyage, de la temperature de deshydratation commencante et des autres caracteristiques physico-chimiques de l'hydrate broye a permis de montrer que la tension superficielle des grains du materiau broye est un facteur d'action preponderant.

An electrical conductivity and transmission electron microscopy study of the very early stages of the sulphurization by H2S of NiO single crystals were carried out at low pressure (p

Les auteurs presentent les effets du broyage par percussion et par abrasion sur les caracteristiques morphologiques, cristallographiques et celles liees a l'etat de surface pour une serie d'oxalates hydrates (CaC2O4 · H2O; K2C2O4 · H2O; BaC2O4 · nH2O avecn=0, 1/2, 1 et 2). Il apparait notamment que hormis les modifications de taille et des proprietes superficielles des cristallites, le broyage provoque des le debut du traitement des distorsions reticulaires importantes. Ces dernieres s'attenuent tres curieusement avec la duree du broyage mais elles reapparaissent, dans certains cas, apres plusieurs heures de traitement. La signification de telles fluctuations, observees aussi pour l'etat de cristallisation des sels broyes par abrasion, est discutee. Un rapprochement est fait entre les dimensions limites des grains d'hydrate auxquelles on aboutit par broyage et celles des cristallites obtenus par thermolyse de ces memes hydrates.

Some anomalies observed in the dielectric properties of ceramics made from calcines of BaTiO3 are due to the presence of Ba2TiO4. These effects are only negligible if the Ba2TiO4 concentration in the calcine is less than 1 or 2 wt %. For concentrations greater than this, Ba2TiO4 inhibits the growth of BaTiO3 grains, shifts the Curie point towards low temperatures, decreaseser and causes large fluctuations in tanδ curves.

Le comportement thermique d'un melange ternaire 94% BaTiO3–5% CaZrO3–0,6% Nb2O5 (% massiques) a ete etudie entre 1225 et 1450 °C par mesure des parametres cristallins et de la composition elementaire des deux solutions solides constituant les ceramiques apres frittage. Il apparaǐt que ces deux solutions, du type (Ba1–xCax) (Ti1–yZry)O3, sont cristallographiquement proches du metatitanate quadratique et le demeurent měme aux temperatures les plus elevees. Les grains d'une měme solution solide n'ont pas tous la měme composition. Cette inhomogeneite s'amenuise lorsque la temperature croǐt et l'on a constate que la composition en ions tetravalents s'homogeneise beaucoup plus rapidement que celle en ions divalents. The thermal behavior of the ternary mixture 94% BaTiO3–5% CaZrO3–0.6% Nb2O5 is studied between 1225 and 1450 °C by X-ray diffraction and quantitative microprobe analysis. In the above range of temperature ceramics are formed of two solid solutions (Ba1–xCax) (Ti1–yZry)O3 structurally close to the tetragonal BaTiO3. For each of the two phases, the elementary composition is different from one grain to another. The inhomogeneity tends to disappear when the temperature increases, but the tetravalent ion composition changes more rapidly than that of the divalent ions. The same analysis, made on the binary mixing 95% BaTiO3-5% CaZrO3, shows that this peculiarity is due to a chemical effect of the Nb2O5 oxide during the sintering.

A number of studies have shown the existence of orientation relationships in Solid l → Solid 2 + gas — type transformations, concerning mineral solids. Little research has been done to know the way in which the structural edifice rearranges, as has been done for metals and metal alloys. This problem has been the aim of the present investigation considering both the following reactions

Tris(trimethylammonium) heptabromodicadmate [(CH3)3NH]3Cd2Br7 is hexagonal, space group P6mcc. Unit-cell dimensions are: a = 14.863 (6), c = 6.869 (3) A. Powder diffraction data are given.