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We present an electron microscopy and diffraction study of a Ca x Ba 1 − x Nb 2 O 6 ceramic with x = 0.28 (CBN28), a ferroelectric material with a partially filled tetragonal tungsten-bronze structure. The microstructure has strong similarities to that of Sr x Ba 1 − x Nb 2 O 6 , with an average orthorhombic symmetry and an intimate intermixture of merohedral twin variants at a length scale of tens of nanometers. Superstructure spots in diffraction patterns are displaced by a one-dimensional incommensurate modulation, characterized by a propagation vector δ δ 0. Heating experiments show that δ is strongly coupled to ferroelectric polarization, decreasing as 180 ° ferroelectric domains become more finely spaced and needle-like as the Curie temperature T C is approached during heating and increasing once more above T C. No change in symmetry is observed at T C , consistent with a transition from ferroelectric to antiferroelectric (or ferrielectric) relaxor properties. The superstructure spots and incommensurate modulation disappear ∼ 250 ° C above T C , consistent with polar regions in the material becoming fully transient. [ABSTRACT FROM AUTHOR]

We present an electron microscopy and diffraction study of a Ca x Ba 1 − x Nb 2 O 6 ceramic with x = 0.28 (CBN28), a ferroelectric material with a partially filled tetragonal tungsten-bronze structure. The microstructure has strong similarities to that of Sr x Ba 1 − x Nb 2 O 6 , with an average orthorhombic symmetry and an intimate intermixture of merohedral twin variants at a length scale of tens of nanometers. Superstructure spots in diffraction patterns are displaced by a one-dimensional incommensurate modulation, characterized by a propagation vector δ δ 0. Heating experiments show that δ is strongly coupled to ferroelectric polarization, decreasing as 180 ° ferroelectric domains become more finely spaced and needle-like as the Curie temperature T C is approached during heating and increasing once more above T C. No change in symmetry is observed at T C , consistent with a transition from ferroelectric to antiferroelectric (or ferrielectric) relaxor properties. The superstructure spots and incommensurate modulation disappear ∼ 250 ° C above T C , consistent with polar regions in the material becoming fully transient. [ABSTRACT FROM AUTHOR]

The optical and structural properties of InAs quantum dots with a thin InAlAs-InGaAs composite cap layer are systematically investigated by photoluminescence and transmission electron microscopy. A number of improvements in the optical properties are observed with the use of an InAlAs-InGaAs cap layer, instead of InGaAs.

The microstructural characterization of sol-gel lead-zirconate-titanate thin films was examined using x-ray diffraction, X-ray photoelectron spectroscopy, auger analysis and transmission and scanning transmission electron microscopy. Results revealed that the platinum film is highly oriented with the (111) axis perpendicular to the substrate plane. Effects of employing various crystallization processes on compositional separation and the reasons for its occurrence are presented.

Two multiplication mechanisms for misfit dislocations in strained epitaxial layers were investigated. The results showedthat the spiral and Frank-Read sources necessitate a minimum thickness four times as large as the equilibrium critical thickness. This may be a major factor in the slow relief of strained layers with limited numbers of misfit dislocations.

The digital large‐angle convergent‐beam electron diffraction (D‐LACBED) technique is applied to Ca3Mn2O7 for a range of temperatures. Bloch‐wave simulations are used to examine the effects that changes in different parameters have on the intensity in D‐LACBED patterns, and atomic coordinates, thermal atomic displacement parameters and apparent occupancy are refined to achieve a good fit between simulation and experiment. The sensitivity of the technique to subtle changes in structure is demonstrated. Refined structures are in good agreement with previous determinations of Ca3Mn2O7 and show the decay of anti‐phase oxygen octahedral tilts perpendicular to the c axis of the A21am unit cell with increasing temperature, as well as the robustness of oxygen octahedral tilts about the c axis up to ∼400°C. The technique samples only the zero‐order Laue zone and is therefore insensitive to atom displacements along the electron‐beam direction. For this reason it is not possible to distinguish between in‐phase and anti‐phase oxygen octahedral tilting about the c axis using the [110] data collected in this study. [ABSTRACT FROM AUTHOR]

The digital large‐angle convergent‐beam electron diffraction (D‐LACBED) technique is applied to Ca3Mn2O7 for a range of temperatures. Bloch‐wave simulations are used to examine the effects that changes in different parameters have on the intensity in D‐LACBED patterns, and atomic coordinates, thermal atomic displacement parameters and apparent occupancy are refined to achieve a good fit between simulation and experiment. The sensitivity of the technique to subtle changes in structure is demonstrated. Refined structures are in good agreement with previous determinations of Ca3Mn2O7 and show the decay of anti‐phase oxygen octahedral tilts perpendicular to the c axis of the A21am unit cell with increasing temperature, as well as the robustness of oxygen octahedral tilts about the c axis up to ∼400°C. The technique samples only the zero‐order Laue zone and is therefore insensitive to atom displacements along the electron‐beam direction. For this reason it is not possible to distinguish between in‐phase and anti‐phase oxygen octahedral tilting about the c axis using the [110] data collected in this study. [ABSTRACT FROM AUTHOR]