Ruyan Guo

Bio: Ruyan Guo is an academic researcher from University of Texas at San Antonio. The author has contributed to research in topics: Dielectric & Ferroelectricity. The author has an hindex of 40, co-authored 441 publications receiving 9707 citations. Previous affiliations of Ruyan Guo include Armenian National Academy of Sciences & Zhejiang University.

The perovskite structure—a review of its role in ceramic science and technology

Abstract: Starting with the history of the fundamental science of the relation of structure to composition delineated completely by Goldschmidt, we use the perovskite structure to illustrate the enormous pow...

Origin of the high piezoelectric response in PbZr1-xTixO3

Abstract: High resolution x-ray powder diffraction measurements on poled PbZr1-xTixO3 (PZT) ceramic samples close to the rhombohedral-tetragonal phase boundary (the so-called morphotropic phase boundary) have shown that for both rhombohedral and tetragonal compositions the piezoelectric elongation of the unit cell does not occur along the polar directions but along those directions associated with the monoclinic distortion. This work provides the first direct evidence for the origin of the very high piezoelectricity in PZT.

Tetragonal-to-monoclinic phase transition in a ferroelectric perovskite : The structure of PbZr0.52Ti0.48O3

Abstract: The perovskitelike ferroelectric system ${\mathrm{PbZr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}$ (PZT) has a nearly vertical morphotropic phase boundary (MPB) around $x=0.45--0.50.$ Recent synchrotron x-ray powder diffraction measurements by Noheda et al. [Appl. Phys. Lett. 74, 2059 (1999)] have revealed a monoclinic phase between the previously established tetragonal and rhombohedral regions. In the present work we describe a Rietveld analysis of the detailed structure of the tetragonal and monoclinic PZT phases on a sample with $x=0.48$ for which the lattice parameters are, respectively, ${a}_{t}=4.044$ \AA{}, ${c}_{t}=4.138$ \AA{}, at 325 K, and ${a}_{m}=5.721$ \AA{}, ${b}_{m}=5.708$ \AA{}, ${c}_{m}=4.138$ \AA{}, $\ensuremath{\beta}=90.496\ifmmode^\circ\else\textdegree\fi{},$ at 20 K. In the tetragonal phase the shifts of the atoms along the polar [001] direction are similar to those in ${\mathrm{PbTiO}}_{3}$ but the refinement indicates that there are, in addition, local disordered shifts of the Pb atoms of $\ensuremath{\sim}0.2$ \AA{} perpendicular to the polar axis. The monoclinic structure can be viewed as a condensation along one of the $〈110〉$ directions of the local displacements present in the tetragonal phase. It equally well corresponds to a freezing-out of the local displacements along one of the $〈100〉$ directions recently reported by Corker et al. [J. Phys.: Condens. Matter 10, 6251 (1998)] for rhombohedral PZT. The monoclinic structure therefore provides a microscopic picture of the MPB region in which one of the ``locally'' monoclinic phases in the ``average'' rhombohedral or tetragonal structures freezes out, and thus represents a bridge between these two phases.

Stability of the monoclinic phase in the ferroelectric perovskite PbZr1-xTixO3

Abstract: Recent structural studies of ferroelectric ${\mathrm{PbZr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}$ (PZT) with $x=0.48,$ have revealed a monoclinic phase in the vicinity of the morphotropic phase boundary (MPB), previously regarded as the boundary separating the rhombohedral and tetragonal regions of the PZT phase diagram. In the present paper, the stability region of all three phases has been established from high-resolution synchrotron x-ray powder-diffraction measurements on a series of highly homogeneous samples with $0.42l~xl~0.52.$ At 20 K, the monoclinic phase is stable in the range $0.46l~xl~0.51,$ and this range narrows as the temperature is increased. A first-order phase transition from tetragonal to rhombohedral symmetry is observed only for $x=0.45.$ The MPB, therefore, corresponds not to the tetragonal-rhombohedral phase boundary, but instead to the boundary between the tetragonal and monoclinic phases for $0.46l~xl~0.51.$ This result provides important insight into the close relationship between the monoclinic phase and the striking piezoelectric properties of PZT; in particular, investigations of poled samples have shown that the monoclinic distortion is the origin of the unusually high piezoelectric response of PZT.

Piezoelectric and strain properties of Ba(Ti1−xZrx)O3 ceramics

Abstract: The polarization and strain behavior of Ba(Ti1−xZrx)O3 (x=0–03) ceramics are studied The unipolar strain levels of ∼018% at 40 kV/cm and of ∼025% at ∼120 kV/cm with small hysteresis were obtained for the ceramics with 003⩽x⩽008 The remnant polarization is ∼13–18 μC/cm2 for 003⩽x⩽008 and below 2 μC/cm2 for 015⩽x⩽03 at room temperature The electromechanical coupling coefficient K33=565% and the piezoelectric stain coefficient d33=236 pC/N were obtained for the ceramics with x=005 These results indicated that the Ba(Ti1−xZrx)O3 system is a promising lead-free high strain material for applications

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Abstract: Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Physics and Applications of Bismuth Ferrite

Abstract: BiFeO3 is perhaps the only material that is both magnetic and a strong ferroelectric at room temperature. As a result, it has had an impact on the field of multiferroics that is comparable to that of yttrium barium copper oxide (YBCO) on superconductors, with hundreds of publications devoted to it in the past few years. In this Review, we try to summarize both the basic physics and unresolved aspects of BiFeO3 (which are still being discovered with several new phase transitions reported in the past few months) and device applications, which center on spintronics and memory devices that can be addressed both electrically and magnetically.

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Room-temperature ferroelectricity in strained SrTiO3.

Abstract: Systems with a ferroelectric to paraelectric transition in the vicinity of room temperature are useful for devices. Adjusting the ferroelectric transition temperature (T(c)) is traditionally accomplished by chemical substitution-as in Ba(x)Sr(1-x)TiO(3), the material widely investigated for microwave devices in which the dielectric constant (epsilon(r)) at GHz frequencies is tuned by applying a quasi-static electric field. Heterogeneity associated with chemical substitution in such films, however, can broaden this phase transition by hundreds of degrees, which is detrimental to tunability and microwave device performance. An alternative way to adjust T(c) in ferroelectric films is strain. Here we show that epitaxial strain from a newly developed substrate can be harnessed to increase T(c) by hundreds of degrees and produce room-temperature ferroelectricity in strontium titanate, a material that is not normally ferroelectric at any temperature. This strain-induced enhancement in T(c) is the largest ever reported. Spatially resolved images of the local polarization state reveal a uniformity that far exceeds films tailored by chemical substitution. The high epsilon(r) at room temperature in these films (nearly 7,000 at 10 GHz) and its sharp dependence on electric field are promising for device applications.