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.
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.
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.
With the purpose of improving the dielectric and piezoelectric properties of (K
0.5
Na
0.5
)NbO
3
(KNN), a multiple doping strategy was tested in this research. Piezoceramics with composition (K
0.5
...Na
0.5
)
0.94
Li
0.06
0.97
La
0.01
(Nb
0.9
Ta
0.1
)O
3
were prepared by the traditional ceramic method. The calcined powders were sintered in their own atmosphere at 1,100 °C for 1.0, 1.5 and 2.5 h. X-ray diffraction analysis showed that the Li
+
, La
3+
and Ta
5+
cations diffuse into the KNN structure to form a perovskite-structured solid solution. For 1 h sintering time, a dominant orthorhombic phase is obtained, whereas for the longer times, the dominant phase was tetragonal. The presence of a tetragonal tungsten–bronze minority second phase is confirmed. Scanning electron micrographs show rectangular-shaped grains with a mean size of 1.1 ± 0.2 μm. The existence of pores and traces of a liquid phase favoring grain growth and homogeneity is also observed. Experimental results show an enhancement of the permittivity associated with the enlargement of the
c
parameter of the cell that increases with sintering time. Li
+
incorporation into the structure is made evident by its transition temperature at 400 °C different from those of KNNLaTi (81–110 °C) and KNNLaTa (340 °C). An analysis of the phase transition of the samples indicates a normal rather than a diffuse transition. The electromechanical parameters
k
p
,
Q
m
,
σ
p
,
s
11
,
d
31
and
g
31
are determined and compared to those of commercial PZT ceramics.
The results obtained in the study of (K
0.44
Na
0.52
Li
0.04
)
0.97
La
0.01
Nb
0.9
Ta
0.1
0
3
ceramics obtained by solid state sintering from the precursor NaNbO
3
synthetized by the reactive ...templated grain growth (RTGG) technique are presented. X-ray diffraction studies show the coexistence of two crystals phases, orthorhombic and tetragonal, being the last one, the more abundant. Dielectric measurements make evident the effect of La doping through a decrease in the transition temperatures with respect to those reported for undoped KNN (tetragonal-cubic T
T-C
= 264 °C and orthorhombic -tetragonal T
O-T
= 90 °C. The maximum value for the dielectric permittivity is surprisingly high at 6800 at room temperature and 1 kHz. Piezoforce microscopy (PFM) shows domain switching areas in response to the applied electric field but also non-switching zones where the polarization is perpendicular to the applied field. Hysteresis obtained by PFM shows the effective piezoelectric coefficient d
eff
= 164 pC N
−1
comparable to the best values of PZT and KNN ceramics.
Studies of structural and dielectric properties of lead-free perovskite K
0.5
Na
0.5
NbO
3
(KNN) ceramics obtained by the substitution of 5 at% of La and Ti for ions in the A-site and B-site, ...respectively, and sintered at different temperatures between 1100°C and 1190°C, are presented. X-ray diffraction patterns show the successful formation of an orthorhombic perovskite phase similar to that of pure KNN. The effect of doping and sintering temperature on the dielectric properties of the resulting ceramics is discussed. Simultaneous substitution of La and Ti into the KNN (KNNLaTi) causes a shift in the ferroelectric–paraelectric phase transition temperature from that of pure KNN (420°C) to considerably lower ones (81 to 110°C) for the modified compounds. A particularly important result is the appearance of a single peak in the permittivity vs. temperature curve associated with the ferroelectric–paraelectric phase transition, where the KNNLaTi compound changes from orthorhombic to cubic structure, instead of the two reported for pure KNN. This transition exhibits the characteristics of a normal diffuse phase transition with an incipient relaxer behavior.
The results of ferroelectric properties studies of KNN doped with La and Ti and sintered at temperatures in the interval of 1100 °C–1190 °C are presented in this work. The doping was achieved by the ...substitution of La for ions in A sites and Ti for ions in the B sites. Values of 94 % of the theoretical density were accomplished. The effect of the sintering temperature and the inclusion of the La and Ti cations in the KNN structure is evident through the shift in the ferroelectric-paraelectric transition temperature of ∼110 °C with respect to that of pure KNN (420 °C). Microstructure and ferroelectric analyses were carried out using Piezoresponse Force Microscopy (PFM) and hysteresis loops with interesting results, Δ
P
r
=9 (μC/cm
2
) and
P
r
/
P
max
=0.41, even when the saturation of the materials is not reached.
An electron paramagnetic resonance (EPR) study of FeNbO
4 powder samples in monoclinic phase (wolframite-type) at X-band (8.8–9.8
GHz), in the 90–300
K temperature range, is presented. For all the ...temperatures, the EPR spectrum shows a single line associated with Fe
3+ ions. Changes in the lineshape of the EPR spectrum, which can be attributed to Fe
2+ ions, are detected at low temperatures. This behavior can be ascribed to a strong magnetic dipolar interaction between Fe
2+ and Fe
3+ ions. The non-resonant microwave absorption techniques: magnetically-modulated microwave absorption spectroscopy (MAMMAS) and low-field microwave absorption spectroscopy (LFMAS), were used for a further knowledge on this material. MAMMAS response suggests also the presence of Fe
2+ ions, that originates a change in microwave absorption regime for
T
<
T
p (=140
K), associated with the presence of short-range magnetic correlations. LFMAS spectra showed a linear behavior with positive slope and non-hysteretic traces. The profiles obtained by plotting the slope vs. temperature of the LFMAS line are similar to those detected by the MAMMAS technique, confirming that both types of measurement show the same processes of absorption.
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An electron paramagnetic resonance (EPR) study of ferroelectromagnet Pb(Fe1/2Nb1/2)O3 (PFN) powders is presented. The EPR spectra show a single broad line in the 300-500K temperature range, ...attributable to Fe3+ ions. The onset of the ferro-paraelectric transition was determined from the temperature dependence of three main parameters deduced from the EPR spectra: g-factor, peak-to-peak linewidth and integrated intensity. These parameters indicate a behavior in agreement with a diffuse phase transition.
