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Polycrystalline BiMn2O5 and Bi0.9Ce0.1Mn2O5 have been prepared by a solid-state reaction. A crystalline structure study shows that all x-ray diffraction patterns can be indexed successfully in an orthorhombic phase. Substitution of Ce for Bi ions induced in the unit cell a slight distortion and enlargement. Magnetic and dielectric measurements all reveal that Ce substitution induces great effects: BiMn2O5 is in the antiferromagnetic (AFM) phase with a Néel transition temperature at about 42 K, whereas Bi0.9Ce0.1Mn2O5 is in the ferromagnetic (FM) phase with a Curie temperature at about 46 K. The permittivity of Bi0.9Ce0.1Mn2O5 is much higher than that of BiMn2O5, and two dielectric relaxation peaks have been observed in the former, instead of one dielectric loss peak as observed in BiMn2O5. The valent state of Ce ions has been analyzed mainly as tetravalent by the core-level spectrum of Ce 3d from x-ray photoemission spectroscopy. The possible mechanisms of the magnetic transition from AFM to FM and the peculiar dielectric relaxation peaks induced by Ce substitution have been discussed in detail. [ABSTRACT FROM AUTHOR]

Ba0.5Sr0.5TiO3 (BST) thin films are among the best-known ferroelectric and dielectric materials. Ce-doped BST films have been fabricated by pulsed laser deposition in order to enhance their dielectric properties. X-ray diffraction, atomic force microscopy, and Raman spectroscopy have been used to study variations of crystal structure, surface morphologies, and phase stability of Ce-doped BST films, respectively. A strong influence of Ce doping on the properties of the BST films has been observed. First, a small amount of Ce dopant makes easy epitaxial growth of a BST film with a smooth surface on a MgO substrate. Second, residual stress in a BST film on a MgO substrate can be reduced by Ce doping, as demonstrated by the blueshift of phonon peaks in Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Si–Ba0.5Sr0.5TiO3 composite thin films were deposited by pulsed laser deposition technique on (100) Nb:SrTiO3 substrates. The crystal structure and surface morphology of the thin films have been characterized by x-ray diffraction and atomic force microscopy, respectively. Experimental results suggested that the Si composition has played a positive role in improving the dielectric properties of the thin films. With the increased Si concentration, the dielectric loss was significantly reduced, accompanied with a tolerable reduction of tunability. In particular, the 14% Si composite film exhibited a dielectric loss of 0.005, which is much lower than that of the undoped Ba0.5Sr0.5TiO3 (BST) film. Moreover, a proper concentration of Si in the film improved the figure of merit from 9 of the undoped BST to 23 of 1.4% Si composite films. [ABSTRACT FROM AUTHOR]

A relationship between the temperature and the dielectric strength of a Maxwell–Wagner (MW) type relaxation was deduced based on the conventional two-layer model for inhomogeneous systems and under the usual assumptions that the conductivity of each layer obeys the thermally activated law and the dielectric constant of each layer is relatively temperature independent. The relation shows that the relaxation peak height in the imaginary part of the complex permittivity for a MW-type relaxation increases with decreasing temperature and saturates at low enough temperature. This behavior was well-proved by both numeral and experimental results and therefore could be regarded as a fingerprint of a MW-type relaxation in most practical cases. [ABSTRACT FROM AUTHOR]

Multilayered thin films of (Ba[sub 0.80]Sr[sub 0.20])(Ti[sub 1-x]Zr[sub x])O[sub 3] (BSTZ) with compositionally graded layer (CGL) have been fabricated by pulsed laser deposition on Pt/TiO[sub 2]/SiO[sub 2]/Si substrate. In each CGL, four individual layers of BSTZ with x=0.36, 0.18, 0.08 and 0 are grown in series with equal thickness. Three kinds of thin-film CGL samples comprising one, two or four CGLs have been elaborated with the final same thickness, and the thickness of each CGL is accordingly varied in different samples to achieve the gradients of composition. The crystalline structures of the CGL thin films are successively characterized using x-ray diffraction and their electrical properties such as ac dielectric properties and polarizations are investigated. Improved dielectric properties and tunability of permittivity have been observed in the multilayered CGL films compared to single-layer BSTZ films prepared in the identical condition. Furthermore, with increasing gradients of compositions in the CGL multilayered films, the dielectric permittivity and its tunability increase, and the hysteresis loop of the thin films disappears. The results show that the internal stress produced by the gradient of composition could be a dominant factor to influence the dielectric properties. The improved dielectric properties and tunability for the applications of tunable devices can be obtained by the manipulation of the gradient of compositions in the multilayered films. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Polycrystalline BiMn2O5 and Bi0.9Ce0.1Mn2O5 have been prepared by a solid-state reaction. A crystalline structure study shows that all x-ray diffraction patterns can be indexed successfully in an orthorhombic phase. Substitution of Ce for Bi ions induced in the unit cell a slight distortion and enlargement. Magnetic and dielectric measurements all reveal that Ce substitution induces great effects: BiMn2O5 is in the antiferromagnetic (AFM) phase with a Néel transition temperature at about 42 K, whereas Bi0.9Ce0.1Mn2O5 is in the ferromagnetic (FM) phase with a Curie temperature at about 46 K. The permittivity of Bi0.9Ce0.1Mn2O5 is much higher than that of BiMn2O5, and two dielectric relaxation peaks have been observed in the former, instead of one dielectric loss peak as observed in BiMn2O5. The valent state of Ce ions has been analyzed mainly as tetravalent by the core-level spectrum of Ce 3d from x-ray photoemission spectroscopy. The possible mechanisms of the magnetic transition from AFM to FM and the peculiar dielectric relaxation peaks induced by Ce substitution have been discussed in detail. [ABSTRACT FROM AUTHOR]