Biomedical subjects

Van Tendeloo G

Publications and source records attributed to Van Tendeloo G.

12 recordsLinked to original sources

PubMed2000

Microstructure of Cu(x)Mo6S8 Chevrel phase thin films on R-plane sapphire

Cu(x)Mo6S8 Chevrel phase thin films epitaxially grown on R-plane sapphire substrates have been studied using field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HREM). For samples grown in optimal conditions, the SEM images evidence oriented grains of about 100 nm average size; the HREM images of cross-section samples allow to deduce the local epitaxial relations between the substrates and films. HREM also evidences two grain families, previously deduced from X-ray and reflection high-energy electron diffraction studies. No defects have been observed in the films; a higher molybdenum content in the films results in Mo-precipitation at the film-substrate interface.

Journal Article↗

PubMed1999

The phase transitions and crystal structures of Ba3RM2O7.5 complex oxides (R = rare-earth elements, M = Al, Ga).

The structures of alpha-Ba(3)RAl(2)O(7.5) and beta-Ba(3)RM(2)O(7.5) complex oxides (R = rare-earth elements, M = Al, Ga) have been studied by a combination of X-ray diffraction, electron diffraction (ED) and high-resolution electron microscopy (HREM). The alpha and beta forms have cell parameters related to the perovskite subcell: a = 2a(per), b = a(per)(2)(1/2), c = 3a(per)(2)(1/2), however, the alpha form has an ortho-rhombic unit cell whereas the beta form adopts monoclinic symmetry. The crystal structure of monoclinic Ba(3)ErGa(2)O(7.5) was refined from X-ray powder data (space group P2/c, a = 7.93617(9), b = 5.96390(7), c = 18.4416(2) Å, beta = 91.325(1) degrees, R(I) = 0.023, R(P) = 0.053), the structure of the alpha form (space group Cmc2(1)) was deduced from ED and HREM data. The important feature of the alpha and beta structures is the presence of slabs containing strings of vertex-sharing tetrahedral Al(2)O(7) pairs. Two almost equivalent oxygen positions within the strings can be occupied either in an ordered manner leading to the low-temperature beta phase or randomly resulting in the high-temperature alpha structure. The critical temperature of this order-disorder phase transition was determined by high-temperature X-ray diffraction and by differential thermal analysis (DTA). In situ ED and HREM observations of the second-order phase transition confirmed the symmetry changes and revealed numerous defects (twins and antiphase boundaries) formed during the phase transformation.

Journal Article↗

PubMed1999

Room-temperature and low-temperature structure of Nd1-xCaxMnO3 (0.3 </= x </= 0.5).

The structure of the insulating manganites Nd(1-x)Ca(x)MnO(3) (0.3 </= x </= 0.5) has been studied against temperature using electron diffraction and neutron diffraction. At room temperature, the three compounds with x = 0.3, 0.4 and 0.5 exhibit the orthorhombic GdFeO(3)-type structure (a approximately 2(1/2)a(p), b approximately 2a(p), c approximately 2(1/2)a(p)). Below the charge-ordering temperature of approximately 250 K, a doubling of the lattice is observed along the a axis which could be interpreted as an ordering of the d(z(2)) Mn(3+) orbitals. The low-temperature polymorph has ortho-rhombic symmetry for x = 0.5 and monoclinic symmetry for x = 0.4 and 0.3. The low-temperature structure of the x = 0.4 sample was refined using neutron diffraction data. The HREM study at room temperature confirms the average GdFeO(3)-type structure and indicates the existence of defective areas with a lower symmetry.

Journal Article↗

PubMed1996