The next generation of all-solid-state thin-film energy storage devices, such as supercapacitors and pseudocapacitors, requires a wide operating temperature range to work under demanding conditions. ...We have conducted an electrical study of the Ru/YSZ/Ru thin film device to better understand the nature of the ionic conduction processes during the transition from the super-to pseudocapacitive regime as a function of the temperature. Also, it was correlated the storage characteristics of the device to its electrical properties. The complex modulus analysis indicates increased ion mobility with temperature. A DC bias increased the mobility by three orders of magnitude. The activation energy for the ionic mobility without and with DC bias was 1.06 eV and 1.86 eV, respectively. The difference in energy is attributed to the electrostatic repulsion originated by the decomposition of YSZ, the accumulation of ions and vacancies at interfaces, and reactions at the electrode interfaces. Galvanostatic charge-discharge showed a maximum energy density of 200 mWh/cm3 @170 °C. The transition from a super-to a pseudocapacitive behavior occurs at the temperature where redox reactions initiate at electrodes interfaces, as determined by the equivalent circuits for impedance curves. At this point, the increase of energy density becomes steeper.
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•Bias voltage decreases the response time of oxygen ions.•Bias voltage increases the dielectric constant due to a higher concentration of species.•The accumulated species on the interfaces form compounds with the electrodes that contribute to the total polarization.•Energy density values shift from the supercapacitor to the battery region with increasing operating temperature.
Nuevas piezocerámicas libres de plomo basadas en knn Jorge J. Portelles Rodríguez; Juan Fuentes Betancourt; María Dolores Durruthy ...
Anales de la Academia de Ciencias de Cuba,
01/2022, Letnik:
12, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Introducción. el presente trabajo, muestra la descripción de los métodos de obtención empleados para lograr piezocerámicas libres de plomo KNN dopadas: (K0.5Na0.5)0.95La0.05(Nb0.9Ti0.05)O2.9 y ...(K0.44Na0.52Li0.04)0.97La0.01Nb0.9Ta0.103 y la caracterización física de estos. El objetivo fue adquirir un método de obtención reproducible que propiciará buenas propiedades físico-químicas en los sistemas empleados y emplear nuevos dopantes como el Ti, de un menor precio en el mercado, y el La, no trabajados hasta el momento en la literatura consultada, para modificar y controlar sus propiedades físico-químicas. Métodos. Se emplea un método combinado de reacción del crecimiento del grano, (RTGG), para la obtención del precursor NaNbO3 y partiendo de éste lo hacemos reaccionar mediante estado sólido con los demás reactivos simplificando métodos existentes, y la caracterización: dieléctrica, transiciones de fases, caracterización estructural por Difracción de rayos X, y microscopia de piezofuerza (PFM). Resultados. Se obtienen piezocerámicas dopadas con Ti-La, fotoluminicentes con buena potencia de emisión de luz azul y piezoeléctricas KNN dopadas Li- La-Ta. En ambas composiciones presentadas; el dopar con La, se regula el crecimiento del grano y modifica las propiedades dieléctricas y hace disminuir las temperaturas de transición. En el compuesto KNN dopado con Li-La-Ta se obtiene coexistencia de fases a temperatura ambiente y buenas propiedades dieléctricas y cierta anisotropía en la orientación de los dominios. Los resultados experimentales realizados por (PFM), demuestran excelentes constantes piezoeléctricas def = 166 pCN-1 comparados con las mejores cerámicas PZT. Conclusiones: los resultados presentados potencian la utilización de éstos como emisores de luz ferroeléctricos, así como transductores libres de plomo. Ambas composiciones, aún no se han homologado internacionalmente.
Using Raman spectroscopy, the study of a polymorphic phase transition in the KNNLiTaLa
0.01
compound is presented. An analysis of the behavior with temperature, wavenumber and half width at full ...maximum of the individual bands, corresponding to the vibration modes of the (Nb/Ta)O
6
octahedra of the KNNLiTaLa
0.01
compound's structure, is performed. This analysis determined that the polymorphic phase transition of the KNNLiTaLa
0.01
compound occurs in the 90 to 105°C temperature interval. Using the Hard Mode Spectroscopy method, the value of the critical exponent of the order parameter was determined to be β ≈ ½, indicative of a second order transition.
BaTiO 3 -CoFe 2 O 4 nanocomposites with a 1/1 molar ratio were prepared by a combination of polyol synthesis (chimie douce) and a subsequent consolidation by spark plasma sintering. The nanocomposite ...samples, with a grain size about 50 nm showed a good mixing and a high density. Their impedance response was measured in the 5 Hz-1 MHz frequency range, under magnetic fields up to 1200 kA/m. Measurements were carried out in the 40-210 °C temperature range. We used the Jonscher's universal relaxation law to analyze the electric conductivity results. Significant changes in the activation energies for long range conductivity and hopping conductivity were observed both at the coercive magnetic field of the ferrite and the Curie transition of the titanate. We show that the use of impedance spectroscopy, based on a wide frequency range, provides a far larger view of electric phenomena allowing a separation of the several contributions to the conductivity phenomena, as a function of the magnetic field.
Granular BaTiO3-CoFe2O4 (BTO-CFO) nanocomposites were prepared by combining polyol synthesis and spark plasma sintering (SPS). This method allows samples with a high density and a very small grain ...size (less than 150 nm), and thus a large interface area between phases. In order to study the involved magnetoelectric effects, the impedance response of these nanomaterials was measured in the 5 Hz-10 MHz frequency range, under 0-7.5 kOe magnetic applied fields, and in the 40-170°C temperature range. The best agreement to model these results by an equivalent circuit was achieved by means of three parallel RC arrangements connected in series; by their RC values, these circuits are representative of grain boundaries. An association between each RC circuit and each interface (or grain boundary), i. e., BTO-BTO, BTO-CFO, and CFO-CFO, is proposed on the basis of their temperature and magnetic behavior.
The
values of PZT53/47 doped with 0.6% Gd
2
O
3
show an anomalous behavior near 132°C as a consequence of a ferroelastic transition. A non-linear fit to the experimental data of the elastic stiffness ...variation
shows that it behaves according to the theoretical law describing pseudoproper ferroelastic transitions. Through Raman spectrum analysis, the frequency of soft mode A
1
(1TO) has a minimum in the 132-136°C temperature interval associated with the coupling to the
component of the deformation. The quantitative evaluation of the order parameter by hard mode spectroscopy ratified the occurrence of a ferroelastic phase transition. The behavior of both piezoelectric coefficients d
31
and the electromechanical coupling factor k
31
can be taken as evidence of the transition showing local maxima at 138°C as a consequence of the maximum deformation during the oscillations of the A
1
(1TO) mode.
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