Flexocaloric effect in ferroelectric materials: methods of indirect evaluation

2021 ◽  
Vol 127 (6) ◽  
Author(s):  
Satyanarayan Patel
Keyword(s):  
Ferroelectric Materials ◽  
Indirect Evaluation

Electron Microscope study of commensurate-incommensurate phase transition in BaZnGeO4

1990 ◽  
Vol 48 (4) ◽  
pp. 172-173
Author(s):  
Naoki Yamamoto ◽  
Makoto Kikuchi ◽  
Tooru Atake ◽  
Akihiro Hamano ◽  
Yasutoshi Saito
Keyword(s):  
Phase Transition ◽  
Electron Microscope Study ◽  
Room Temperature ◽  
Hexagonal Lattice ◽  
Ferroelectric Materials ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Periodic Arrays ◽  
Modulation Wave Vector

BaZnGeO4 undergoes many phase transitions from I to V phase. The highest temperature phase I has a BaAl2O4 type structure with a hexagonal lattice. Recent X-ray diffraction study showed that the incommensurate (IC) lattice modulation appears along the c axis in the III and IV phases with a period of about 4c, and a commensurate (C) phase with a modulated period of 4c exists between the III and IV phases in the narrow temperature region (—58°C to —47°C on cooling), called the III' phase. The modulations in the IC phases are considered displacive type, but the detailed structures have not been studied. It is also not clear whether the modulation changes into periodic arrays of discommensurations (DC’s) near the III-III' and IV-V phase transition temperature as found in the ferroelectric materials such as Rb2ZnCl4.At room temperature (III phase) satellite reflections were seen around the fundamental reflections in a diffraction pattern (Fig.1) and they aligned along a certain direction deviated from the c* direction, which indicates that the modulation wave vector q tilts from the c* axis. The tilt angle is about 2 degree at room temperature and depends on temperature.

Investigation of ferroelectrics using conventional and in situ electron microscopy

1994 ◽  
Vol 52 ◽  
pp. 586-587
Author(s):  
V. Saikumar ◽  
H. M. Chan ◽  
M. P. Harmer
Keyword(s):  
Nonvolatile Memory ◽  
Ferroelectric Materials ◽  
Gate Insulator ◽  
Sensors And Actuators ◽  
In Situ Electron Microscopy ◽  
Ferroelectric Domains ◽  
Domain Boundaries ◽  
Domain Interactions ◽  
Memory Applications

In recent years, there has been a growing interest in the application of ferroelectric thin films for nonvolatile memory applications and as a gate insulator in DRAM structures. In addition, bulk ferroelectric materials are also widely used as components in electronic circuits and find numerous applications in sensors and actuators. To a large extent, the performance of ferroelectric materials are governed by the ferroelectric domains (with dimensions in the micron to sub-micron range) and the switching of domains in the presence of an applied field. Conventional TEM studies of ferroelectric domains structures, in conjunction with in-situ studies of the domain interactions can aid in explaining the behavior of ferroelectric materials, while providing some answers to the mechanisms and processes that influence the performance of ferroelectric materials. A few examples from bulk and thin film ferroelectric materials studied using the TEM are discussed below.Figure 1 shows micrographs of ferroelectric domains obtained from undoped and Fe-doped BaTiO3 single crystals. The domain boundaries have been identified as 90° domains with the boundaries parallel to <011>.

The need of electron microscopy in the study of domains and domain walls in ferroelectrics

1994 ◽  
Vol 52 ◽  
pp. 550-551
Author(s):  
Wenwu Cao
Keyword(s):  
Domain Wall ◽  
Domain Walls ◽  
High Mobility ◽  
Continuum Theory ◽  
Polarization Vector ◽  
Ferroelectric Materials ◽  
Dielectric Constants ◽  
Nonlocal Coupling ◽  
Cubic Symmetry ◽  
Gradient Energy

Domain structures play a key role in determining the physical properties of ferroelectric materials. The formation of these ferroelectric domains and domain walls are determined by the intrinsic nonlinearity and the nonlocal coupling of the polarization. Analogous to soliton excitations, domain walls can have high mobility when the domain wall energy is high. The domain wall can be describes by a continuum theory owning to the long range nature of the dipole-dipole interactions in ferroelectrics. The simplest form for the Landau energy is the so called ϕ model which can be used to describe a second order phase transition from a cubic prototype,where Pi (i =1, 2, 3) are the components of polarization vector, α's are the linear and nonlinear dielectric constants. In order to take into account the nonlocal coupling, a gradient energy should be included, for cubic symmetry the gradient energy is given by,

Current uses of intracranial vessel wall imaging for clinical practice: a high-resolution MR technique recently available

2020 ◽  
Vol 78 (10) ◽  
pp. 642-650
Author(s):  
Felipe Torres PACHECO ◽  
Luiz Celso Hygino da CRUZ JUNIOR ◽  
Igor Gomes PADILHA ◽  
Renato Hoffmann NUNES ◽  
Antônio Carlos Martins MAIA JUNIOR ◽  
...  
Keyword(s):  
Clinical Practice ◽  
Vessel Wall ◽  
Vascular Diseases ◽  
Vascular Wall ◽  
Vessel Wall Imaging ◽  
Clinical Settings ◽  
Direct Evaluation ◽  
Intracranial Vessel ◽  
Indirect Evaluation ◽  
Wall Imaging

ABSTRACT Intracranial vessel wall imaging plays an increasing role in diagnosing intracranial vascular diseases. With the growing demand and subsequent increased use of this technique in clinical practice, radiologists and neurologists should be aware of the choices in imaging parameters and how they affect image quality, clinical indications, methods of assessment, and limitations in the interpretation of these images. Due to the improvement of the MRI techniques, the possibility of accurate and direct evaluation of the abnormalities in the arterial vascular wall (vessel wall imaging) has evolved, adding substantial data to diagnosis when compared to the indirect evaluation based on conventional flow analyses. Herein, the authors proposed a comprehensive approach of this technique reinforcing appropriated clinical settings to better use intracranial vessel wall imaging.

Application of global geopotential models to high-precesion levelling processing

2017 ◽  
Vol 926 (8) ◽  
pp. 2-9
Author(s):  
V.V. Popadyev ◽  
D.A. Kuliev
Keyword(s):  
Field Model ◽  
Direct Evaluation ◽  
Gravity Field Model ◽  
Bouguer Anomalies ◽  
Free Air ◽  
Geopotential Models ◽  
Integral Characteristics ◽  
Indirect Evaluation ◽  
Gravity Map ◽  
High Degree

The article studies the properties of the high-degree gravity field model EGM-2008 in the calculation of integral characteristics at large distances several times greater than the spatial resolution of the model. As an example of an indirect evaluation of a high-degree model, a gravimetric correction was computed into the sum of the measured elevations along the line of the high-precision I class leveling of the Krasnovodsk – Chardzhou line located in Turkmenistan. Using the calculator ICGEM, the Bouguer anomalies were calculated at each point of the line, then the attraction of the Bouguer layer (used heights are from catalog) excluded for the transition to free-air anomalies. In parallel, for a direct evaluation of the model, a regular grid of Bouguer anomalies with a step of 2 angular minutes within line area was also obtained, which were then compared with the anomalies from the gravity map J-40 of scale 1

scholarly journals Impedance Spectroscopy of Lead-Free Ferroelectric Coatings

Coatings ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 221
Author(s):  
Mariya Aleksandrova ◽  
Ivailo Pandiev
Keyword(s):  
Composite Coatings ◽  
Electrical Circuit ◽  
Ferroelectric Materials ◽  
Piezoelectric Transducers ◽  
Lead Free ◽  
Electrical Behavior ◽  
Oxide Composite ◽  
Before And After ◽  
Frequency Dependences ◽  
Good Agreement

This paper presents impedance measurements of ferroelectric structures involving lead-free oxide and polymer-oxide composite coatings for sensing and energy harvesting applications. Three different ferroelectric materials grown by conventional microfabrication technologies on solid or flexible substrates are investigated for their basic resonant characteristics. Equivalent electrical circuit models are applied to all cases to explain the electrical behavior of the structures, according to the materials type and thickness. The analytical results show good agreement with the experiments carried out on a basic types of excited thin-film piezoelectric transducers. Additionally, temperature and frequency dependences of the dielectric permittivity and losses are measured for the polymer-oxide composite device in relation with the surface morphology before and after introduction of the polymer to the functional film.

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