Direction Of Composition Gradient Research Articles

Concentration-gradient-driven anisotropic spinodal decomposition kinetics: nitriding of metallic alloys

ABSTRACT The effect of crystallographically oriented, unidirectional concentration gradients on spinodal decomposition in cubic crystalline solids with elastic and interfacial energy anisotropy is discussed. Phase-field simulations reveal that the kinetics of spinodal decomposition occurring in such systems is dependent on the degree of misorientation between the direction of composition gradient and the preferred crystallographic orientation for growth of spinodal fluctuations; the larger is the misorientation, the slower the kinetics. This phenomenon has been used to explain the well-known grain-orientation-dependent N-uptake kinetics observed during nitriding of metallic alloys. Several plausible causes have been proposed in the literature for the grain-orientation-dependent N-uptake kinetics during nitriding. However, this study reveals that this phenomenon is observed exclusively and without exception in alloy systems having a spinodal instability. The N-uptake kinetics in such systems is known to be dependent on the kinetics of spinodal decomposition. Consequently, anisotropic spinodal decomposition kinetics occurring owing to the presence of a surface-directed N-composition gradient in poly-crystalline metals has been shown to be a more fundamental cause for the phenomenon.

Electrical polarization induced by atomically engineered compositional gradient in complex oxide solid solution

Control of inhomogeneity in materials in order to avoid unexpected effects to the system remains a challenge. In this study, we seek to engineer inhomogeneity in materials and anticipate new properties. Through precise control of composition at the atomic scale, an electrical polarization is induced in the composition-graded LaAlO3–SrTiO3 solid solution epitaxially deposited on NdGaO3 substrates. By tailoring the direction of compositional gradient, the relationship between structure and electrical polarization is simulated via phase-field modeling and revealed by a combination of scanning transmission electron microscopy and scanning probe microscopy. The analysis of the results indicates that the induced polarization is due to the flexoelectric effect in the compositional gradient system. The results of this study provide a new pathway for obtaining a new material genome. Moreover, by a suitable design of the new genome, that is, by using different combinations of compositional gradient geometries, local conduction can be obtained and manipulated, providing a new approach to obtain the desired properties.

COMBINATORIAL PREPARATION AND FERROELECTRIC PROPERTIES OF COMPOSITIONALLY GRADIENT PZT THIN FILMS

Using a combinatorial synthesis process, compositionally gradient PZT thin films were conveniently prepared by a chemical solution decomposition (CSD) method. The thin films showed a perovskite structure with (111)-preferred orientation and a thickness of around 450 nm. The surface morphology and ferroelectric properties were significantly different, depending on the direction of compositional gradient. The detailed composition and gradient of the composition was seen to affect the property of compositionally gradient PZT thin films. The gradient thin film PZT654, with a Zr:Ti ratio of 6:4 at the bottom of the film nearest to the substrate, and with an total composition around the morphotropic phase boundary (MPB, x = 0.52) showed favorable ferroelectric properties. However, no typical offset of the hysteresis loops was observed in our work.

Scanning Raman Spectroscopy for Characterizing Compositionally Spread Films

Composition-spread La(1-x)SrxMnO3 thin films were prepared by pulsed laser deposition technique from LaMnO3 and SrMnO3 targets. The films were epitaxial with a continuous variation of the out-of-plane lattice parameter along the direction of composition gradient. Scanning Raman spectroscopy has been employed as a nondestructive tool to characterize the composition-spread films. Raman spectra showed the variation of the structural, Jahn Teller distortions and the presence of coexisting phases at particular compositions that are in agreement with the previous observation on the single-crystal samples. Raman spectra on the continuous composition-spread film also reveal the effect of disorder and strain on the compositions.

Microwave Properties of Compositionally Graded (Ba, Sr)TiO 3 Thin Films for Electrically Tunabel Microwave Devices

Compositionally graded ferroelectric thin films have execellent dielectric properties and abnormal ferroelectric properties which can be used in various microelectronic devices. Compositionally graded (BaSr)TiO 3 [BST] thin films were prepared on MgO substrates by pulsed laser deposition. The crystalline orientation and microstructure of graded BST thin films were studied using x-ray diffraction, scanning electron microscopy. The microwave properties of the graded BST films were investigated as a function of the direction of composition gradient with respect to substrate. Also, we report on the fabrication and performance of coplanar ferroelectric phase shifters. Coplanar waveguide(CPW) type phase shifters have been fabricated on the graded BST/MgO using Au/Cr metal electrodes. The phase shifters were tested at frequencies up to 20 GHz

Microwave Properties of Compositionally Graded (Ba, Sr)TiO 3 Thin Films for Electrically Tunabel Microwave Devices

Compositionally graded ferroelectric thin films have execellent dielectric properties and abnormal ferroelectric properties which can be used in various microelectronic devices. Compositionally graded (BaSr)TiO 3 [BST] thin films were prepared on MgO substrates by pulsed laser deposition. The crystalline orientation and microstructure of graded BST thin films were studied using x-ray diffraction, scanning electron microscopy. The microwave properties of the graded BST films were investigated as a function of the direction of composition gradient with respect to substrate. Also, we report on the fabrication and performance of coplanar ferroelectric phase shifters. Coplanar waveguide(CPW) type phase shifters have been fabricated on the graded BST/MgO using Au/Cr metal electrodes. The phase shifters were tested at frequencies up to 20 GHz