Structural properties of mixed conductor Ba1−xGd1−yLax+yCo2O6−δ

BaGdLaCoO (BGLC) compositions with large compositional ranges of Ba, Gd, and La have been characterised with respect to phase compositions, structure, and thermal and chemical expansion. The results show a system with large compositional flexibility, enabling tuning of functional properties and thermal and chemical expansion. We show anisotropic chemical expansion and detailed refinements of emerging phases as La is substituted for Ba and Gd. The dominating phase is the double perovskite structure Pmmm, which is A-site ordered along the c-axes and with O vacancy ordering along the b-axis in the Ln-layer. Phases emerging when substituting La for Ba are orthorhombic Ba-deficient Pbnm and cubic LaCoO-based R3̄c. When La is almost completely substituted for Gd, the material can be stabilised in Pmmm, or cubic Pm3̄m, depending on thermal and atmospheric history. We list thermal expansion coefficients for x = 0-0.3, y = 0.2.The research has been supported by the National Science Centre Poland (2016/22/Z/ST5/00691), the Spanish Ministry of Science and Innovation (PCIN-2017-125, RTI2018-102161 and IJCI-2017-34110), and the Research Council of Norway (Grant no. 272797 “GoPHy MiCO”) through the M-ERA.NET Joint Call 2016. The authors acknowledge the skilful assistance from the staff of the Swiss–Norwegian Beamline (SNBL) at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. Dr. Cheng Li at POWGEN, SNS, Oak Ridge, US and Dr. Chiu C. Tang at beamline I11 at Diamond, Didcot, UK are gratefully acknowledged for PND and SR-PXD measurements, respectively

Mechanisms of void formation in Ge implanted SiO2 films

The present paper reports on annealing of Ge implanted SiO2 films and emphasize the observation of voids and the mechanism behind their formation which is considered new. Samples were prepared by ion implanting fluences of 3×1016 and 1×1017 cm-2 respectively of 100 keV Ge into amorphous SiO2 films which were subsequently annealed up to 1000 °C in a N2 atmosphere. The structure of the films was studied by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS). The most striking of the observations is that spherical voids with diameters up to tens of nanometers are observed in the films after annealing at 1000 °C for 1 h. The volume fraction of voids increases with the Ge fluence. The mechanism behind the void formation is indicated by the evolution of the sample structure after increasing annealing time or temperature; Ge first segregates into nanocrystals which then increase in size by diffusion and Oswald ripening. Ge is quite mobile in SiO2, and as oxygen or moisture from the annealing atmosphere diffuse in from the surface, the Ge will be bonded in an oxide closer to the surface than the precipitate. There is thus a net flux of Ge out of the nanoprecipitate into an oxide closer to the surface. The volume occupied by the Ge precipitate becomes a void. This model is discussed and it is concluded that it fits the observations. We also report on the filling of the voids by beam induced migration under TEM electron beam exposure

Structure and water uptake in BaLnCo2O6−δ (Ln =La, Pr, Nd, Sm, Gd, Tb and Dy)

The structure of BaLnCoO (Ln =La, Pr, Nd, Sm, Gd, Tb and Dy) was studied by the means of synchrotron radiation powder X-ray diffraction, neutron powder diffraction and Transmission Electron Microscopy (TEM), while water uptake properties were analysed with the use of thermogravimetry (TG) and water adsorption isotherms. The structure refinement revealed that the dominant phase in all compositions was orthorhombic with an ordering of the A-site cations along the c-axis and ordering of oxygen vacancies along the b-axis, which was also directly evidenced by TEM. It was shown that both unit cell volume and average Co-oxidation state at room temperature decrease linearly with decreasing Ln radius. TG water uptake experiments in humidified N–O gas mixture at 300 °C revealed that among all compositions, only BaLaCoO and BaGdCoO exhibit significant water uptake. Surface water adsorption studies showed that the α, a normalised parameter reflecting the surface hydrophilicity, mostly independently of Ln radius was close to 0.5, which means that the surface is neither hydrophobic nor hydrophilic. The results indicated that water uptake observed at 300 °C is a bulk process, which cannot be described by standard hydration/hydrogenation reaction and it is related to the layered structure of the perovskite lattice and characteristic to La or Gd being present in the lattice.The research has been supported by the National Science Centre Poland (2016/22/Z/ST5/00691), the Spanish Government (PCIN-2017-125), and the Research Council of Norway (Grant nᵒ 272797 “GoPHy MiCO”) through the M-ERA.NET Joint Call 2016. Funding from the Spanish Government (RTI2018-102161 and IJCI-2017-34110 grant) is kindly acknowledged. The authors acknowledge the skilful assistance from the staff of the Swiss–Norwegian Beamline (SNBL), at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. Dr Cheng Li is at POWGEN, SNS, Oak Ridge, US and Dr Chiu C. Tang at beamline I11 at Diamond, Didcot, UK are gratefully acknowledged for PND and SR-PXD measurements, respectively, of BaGdCo2O6-δ. SLW and AMG acknowledge the CERIC-ERIC Consortium for the access to experimental facilities and the financial support (No 20187079). CG and MCI acknowledge the financial support from Romanian Ministry of Research and Innovation in the frame of the Core Program PN19-03. SLW would like to express gratitude to Małgorzata Nadolska from Gdańsk University of Technology for support in surface measurements and analysis