Schematic diagram of structural phases identified in the solid solution series as functions of composition and temperature.
Perspective views of the structures encountered in the solid solution series. groups are represented by octahedra, wherein the Ti cation lies at the centre and oxygen ions are located the apices. The spheres represent the ions and the darker and lighter spheres in the structures in (b) and (d), representing layers with greater and lesser occupancy as occur in the ordered structures. Octahedral tilting can be seen in the structures shown in (c) and (d). The unit cell is outlined in each case. These figures were prepared using ATOMS Version 5.0.7 (Eric Dowty, 1999) (a) , (b) , (c) , and (d) .
Zone axis SAED patterns of perovskites with La contents of (a) , (b) , (c) , and (d) . The patterns of [(a) and (d)] the and samples show the expected symmetry ( and , respectively). SAED patterns of [(b) and (c)] the and the samples show reflections which are forbidden by the long-range tetragonal symmetry indicated by neutron and x-ray diffraction.
SAED pattern of the zone axis of tetragonal at room temperature. The relative orientations of the tetragonal axes and cubic “sublattice” are shown. Maxima are indexed according to the cubic sublattice. The circled maxima are forbidden by the nominal tetragonal symmetry of the sample. Similar forbidden maxima are found in samples with , with the intensity of forbidden maxima increasing with . Forbidden maxima lying on the  and  directions are due to cation ordering and so indicate short-range order in samples with .
Systematic row SAED patterns: BF and DF images of perovskites with La contents of [(a)–(c)] 0.2, [(d)–(f)] 0.45, [(g)–(i)] 0.5, [(i)–(l)] 0.6. Each column of data comes from a single area of a single grain of one composition. [(b), (e), (h), and (k)] The BF images were taken, while [(a), (d), (g), and (j)] the grain of interest had the orientation shown in the SAED patterns and were taken, as implied, using only the (000) central BF maximum. The grains were then tilted until the arrowed reflections in each SAED pattern were the brightest reflection in the systematic row, then DF images were taken. [(a)–(c)] The sample shows tetragonal symmetry (no forbidden maxima in SAEDs) and no domain structures in DF imaging. Samples with [(d)–(f)] and [(g)–(i)] show domain structures ( and greater than in size, respectively) in DF imaging, which give rise to forbidden maxima in SADPs and the previously observed broad peaks in XRD and neutron diffraction patterns. [(j)–(l)] The sample is orthorhombic (due to long range cation/vacancy ordering) and hence shows no domain structures in DF imaging.
Part of a series of SAED patterns typical of those used to determine . (a) , (b) , (c) and (d) .
vs data for seven perovskite compositions.
vs La (and vacancy) content.
, , and values for some perovskites.
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