Rongjuan Wang

Direct observation of a fully strained dead layer at Ba0.7Sr0.3TiO3∕SrRuO3 interface

Epitaxial SrRuO3∕Ba0.7Sr0.3TiO3 (BST)/SrRuO3 thin film capacitors were prepared on SrTiO3 substrates by pulsed laser deposition. The structures of stacked BST films with different thicknesses were investigated by transmission electron microscopy. A distinctive layer of about 3nm of thickness was identified within BST films thicker than 9nm at the interface with the SrRuO3 bottom electrode. The distinctive layer is misfit dislocation-free showing pseudoconstant lattice parameters. Misfit dislocations are formed at the interface between the distinctive layer and the BST film bulk layer relaxing the latter as the film thickness increases. The effect of the distinctive layer on the system dielectric response is discussed within the framework of an interfacial dead-layer model.

Interfacial and microstructural properties of SrTiO3 thin films grown on Si(001) substrates

The microstructure and interfaces of SrTiO3 thin films directly deposited by metalorganic chemical vapor deposition on silicon (001) substrates were investigated by means of Bragg-diffraction contrast and high-resolution transmission electron microscopy. The observation of the plan-view specimens showed that the SrTiO3 films are polycrystalline with randomly oriented grains. An amorphous layer was observed at the interfaces between the films and the substrates. The growth kinetics of this amorphous layer was investigated in detail. The thickness showed a rapid initial increase, which is much faster than the corresponding growth of amorphous SiO2 in the absence of precursors, and apparently approaches saturation after a short time. The thickness of the interfacial layer increases with the oxygen partial pressure during deposition and a reduction to a value acceptable for gate-oxide applications has been achieved for the minimum pressure given by the oxygen content of the present precursors. However, this c...

Microstructure of epitaxial Ba0.7Sr0.3TiO3∕SrRuO3 bilayer films on SrTiO3 substrates

The thickness evolution of the microstructure of epitaxial Ba0.7Sr0.3TiO3 thin films grown on SrRuO3∕SrTiO3 was investigated by means of transmission electron microscopy. Within the Ba0.7Sr0.3TiO3 layer, a layered structure (three sublayers) is distinguished as for the configuration of lattice strain and defects. The first sublayer extends for 3nm from the lattice-coherent Ba0.7Sr0.3TiO3∕SrRuO3 interface. The second 13-nm-thick sublayer forms a semicoherent interface with the first sublayer due to the creation of a misfit dislocation network. The third sublayer extends beyond the second sublayer exhibiting a structure characterized by compact columnar features. Planar defects are formed at the boundaries between such features. The formation of a layered structure within the Ba0.7Sr0.3TiO3 films is discussed in the light of the growth modes of films on lattice-mismatched substrates.

Diffuse scattering in decagonal Al–Ni–Fe

Significant diffuse scattering close to Bragg reflections was observed in decagonal Al(71.5)Ni(23.5)Fe(5) phase which is otherwise free of disorder phenomena. As found by synchrotron measurements (DESY, RASYLAB) this diffuse scattering is anisotropically distributed and dumb-bell shaped with a major extension parallel to the scattering vector Q and a typical 1/q(2) fall-off of the diffuse wings. The diffuse data were tentatively interpreted in frame of a TDS theory [Phys. Rev. B 59 (1999) 8221 using only 2 (out of 5) phonon elastic constants, c(11) and c(66). A remarkable matching of observed and calculated diffuse data could be achieved, however, with an unusual (?) c(66)/c(11) ratio equal to 4.0. An alternative interpretation is based on strain fields caused by static lattice distortions [Phys. Rev. B 37 (1988) 4458]. Possibly there is a superposition of both contributions

Reversible phase transition and structure memory effect of metastable phase in electron-irradiated poly(vinylidene-fluoride-trifluoroethyline) copolymers

We report the results of x-ray diffraction studies on phase transition behavior of irradiated poly(vinylidene-fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer. It is found that the transformations between the polar ferroelectric phase, the metastable paraelectric phase, and normal paraelectric phase induced by thermal and electric field are reversible. The reversible phase transition of the metastable paraelectric phase is very important to explain the appearance of giant strain in the irradiated P(VDF-TrFE) copolymer. The macroscopic strain caused by these reversible transitions was estimated.

Phase transition and critical behavior of spin–orbital coupled spinel ZnV2O4*

We present the temperature-dependent susceptibility and specific heat measurement of spinel ZnV2O4. The structural transition with orbital ordering and the antiferromagnetic transition with spin ordering were observed at 50 K and 37 K, respectively. By analysis of the hysteresis behavior between the specific heat curves obtained in warming and cooling processes, the structural transition was confirmed to be the first-order transition, while the antiferromagnetic transition was found to be of the second-order type. At the structural transition, the latent heat and entropy change were calculated from the excess specific heat, and the derivative of pressure with respect to temperature was obtained using the Clausius–Clapayron equation. At the magnetic transition, the width of the critical fluctuation region was obtained to be about 0.5 K by comparing with Gaussian fluctuations. In the critical region, the critical behavior was analyzed by using renormalization-group theory. The critical amplitude ratio A+/A− = 1.46, which deviates from the 3D Heisenburg model; while the critical exponent α is −0.011, which is close to the 3D XY model. We proposed that these abnormal critical behaviors can be attributed to strong spin–orbital coupling accompanied with the antiferromagnetic transition. Moreover, in the low temperature range (2–5 K), the Fermi energy, the density of states near the Fermi surface, and the low limit of Debye temperature were estimated to be 2.42 eV, 2.48 eV−1, and 240 K, respectively.

Phase transition and critical behaviors of spin-orbital coupling spinel compound CdV2O4

The temperature dependent susceptibility and specific heat of spinel compound CdV2O4 were investigated. The structural transition accompanied with orbital order appearing at 89.6 K is confirmed to be a first order transition, while the magnetic transitions at 30.2 K is revealed to be a second order one. For the paramagnetism-antiferromagnetic transition, the width of critical region was estimated to be about 1.5 K by differentiating with Gaussian fluctuation. In critical region, the critical behavior of specific heat was compared with renormalization-group theory. Critical exponent α and critical amplitude ratio (A+/A−) fitting to the data was found to be −0.017 and 1.26, respectively. The value of A+/A− shows the critical behavior of CdV2O4s deviates from 3D-Heisenberg and shifts to 3D-XY. The analysis of specific heat in low temperature range gives out that Debye temperature ΘD for CdV2O4 is estimated to be 190 K.