Pure K
0.5
Na
0.5
NbO
3
(KNN) and KNN doped with Li
+
(6% mole), La
3+
(1.66%, 5%, 6% mole), and Ti
4+
(10% mole) were prepared by mixture of oxides using high-energy milling and conventional ...solid-state reaction. The effects of the dopant on the physical properties of pure KNN have been evaluated based on the structural, ferroelectric, pyroelectric, and dielectric measurements. The XRD measurements show that KNN pure sample contains a mixture of monoclinic and orthorhombic crystalline phases, with a slightly higher concentration of monoclinic phase. In contrast, all doped samples show a higher concentration of the orthorhombic phase, as well as the presence of a secondary phase (K
6
Nb
10.8
O
30
), also detected by Raman measurements. The samples with a higher concentration of this secondary phase, also present greater dielectric losses and lower values of remnant polarization. The dielectric measurements allowed us to detect temperatures of structural transitions (orthorhombic-tetragonal, O-T) previous to the ferroelectric-paraelectric transition (tetragonal-cubic, T-C), and also in this set of samples, a direct correlation was found between the values of remnant polarization and the corresponding pyroelectric signal response.
This study presents the photoluminescence characteristics of the PZT 53/47 system doped at A and/or B sites, with Nb (PZTN), La (PLZT), and Nb–La (PLZTN) in the concentration range from 0.2 to 1.0 ...molar fraction. The intensity of the emission bands of the system PZTN is two orders higher than the intensity of the emission bands of the systems PLZT and PLZTN, and these emission bands are located at 1.73 eV (718 nm), 2.56 eV (485 nm), and 2.93 eV (424 nm). The origin of the luminescence in these systems is associated with lead and oxygen vacancies produced during the sintering process. The results from X-ray diffraction (XRD) show a mixture of rhombohedral and tetragonal phases. The system PZTN shows a higher tetragonal phase concentration, while PLZT and PLZTN systems show a higher rhombohedral phase concentration. The cell volume shows an increase with dopant concentration only in the case of the PLZTN system. The band gap energy shows a small variation in the PZTN and PLZTN cases around 3.0 eV, a close value to the band gap energy of the pure PZT 53/47 sample. The system PLZT shows an increasing behavior until 4.41 eV for the higher dopant concentration.
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.
► ICP-OES method has been developed for analysis of PZT ceramics. ► Influence of operating parameters on SBR, net signal intensity and matrix effect was studied. ► Some lines with an anomalous ...behaviour were observed. ► The precision of analysis ranged from 3 to 13%. ► The accuracy was from 90 to 110%.
An inductively coupled plasma optical emission spectrometry quantification method for the determination of Al, Ca, Cr Cu, Fe, Mn, Mg, Ni, Zn, Ba, K, In and Co in lead zirconate-titanate (PZT) ceramics, modified with strontium and chromium, was developed. Total digestion of ceramics was achieved with a HNO3, H2O2 and HF (ac) mixture by using a microwave furnace. The sensitivity of the net signal intensity respect to radiofrequency power (P) and nebulizer argon flow (FN) variations was strongly dependent of the total excitation energy of line (TEE). For lines with TEE near metastable atoms and ions of argon, an increment of the sensitivities to P and FN variation was observed. At robust plasma conditions the matrix effect was reduced for all matrices and analytes considered. The precision of analysis ranged from 3 to 13%, whereas the analytes recoveries in the spiked samples varied, mostly, from 90 to 110%. The detection limits of studied elements were from 0.004 to 10mgkg−1.
A structural and physical properties study on ferroelectric (K0·44Na0·52Li0.04)0.97La0·01Nb0·9Ta0·1O3 ceramics with monocrystalline grains of orthorhombic (O) and tetragonal (T) perovskite phases ...coexisting at room temperature (RT) is presented. Different sintering temperatures were evaluated. XRD analysis demonstrates high crystalline quality of both phases with volume fractions depending of the sintering temperature. SEM shows grain facets and morphologies of both phases in all samples. Raman analysis confirms the dopant incorporation and the coexistence of both phases. The contributions of each phase in the dielectric response are deconvoluted using the frequency-temperature dielectric analysis. The orthorhombic-to-tetragonal (TO-T) and tetragonal-to-cubic (TT-C) phase transition temperatures shift ~100 °C below those reported for pure-KNN in all samples, as consequence of the Li, La, and Ta doping combination. Li doping promotes T-phase grain growth and decreases TO-T below RT. La incorporation promotes the O-phase grain growth and decreases TO-T and TT-C. The optimal sintering temperature is 1180 °C with 50-50 volume fractions of T-O phases. Piezoresponse studies show a complex 180°-domain structure.
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•Lead free Li/La doped KNNTa ceramic is constituted by coexisting tetragonal and orthorhombic structured grains.•Li doping promotes tetragonal grain growth and La incorporation promotes the orthorhombic grain growth.•Li and La combination shifts the FE-FE transition below room temperature.•The coexistence of two phases provides better room temperature functionality for applications.
In the previous years the ferroelectrics perovskites has shown an increase in the study for optical applications. What do materials take advantage of, the so-called soft or hard dopants? In this work ...we try to clarify some of these aspects analyzing a classic perovskite-type structure system like
Pb
0.95
Sr
0.05
(
Zr
0.53
Ti
0.47
)
1−
y
Cr
y
O
3−
y
/2
(PSZTC) and
Pb
1−3
x
/2
La
x
(
Zr
0.53
Ti
0.47
)
1−
y
Nb
y
O
3−
y
/2
(PLZTN), hard and soft respectively. Photoluminescence, optical absorption spectroscopy, Raman spectroscopy, structural and micro-structural measurements have been carried out. The results revealed the role of the Cr, La and Nb ion substitutions in photoluminescence spectra, energy gap, Raman response, morphology grain size and the symmetry presented in these materials near the morphotropic phase boundary (MPB).
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 microstructural (XRD and SEM) and dielectric behavior of Pb(Zr
0.54
Ti
0.46
)O
3
(PZT 54/46) ceramic system with donor (La, Nb and
La
+
Nb
) doping was studied. For all Nb-doped PZT samples, only ...one (tetragonal) phase was found, which confirms the compositional shifts near the morphotropic phase boundary. For La- and La+Nb-doped samples, there are two (rhombohedral and tetragonal) phases. Dielectric characteristic behavior (1/
ε
) for La- and
La
+
Nb
-doped PZT was associated with two-phase transitions: Ferro–Ferro at low temperature and Ferro–Para at Curie temperature. For Nb-doped samples, only one phase transition is observed, which indicates the presence of a single ferroelectric phase.
In this work, the results of the study on the optical properties of the perovskite structure ABO
3
with La
3+
substitution for ions K
+
and Na
+
in the A site and Ti
4+
substitution for ion Nb
5+
in ...the B site are presented. The ceramics were sintered at 1100°C and 1190°C and formed at 10 MPa and 80 MPa. Dense ceramics were obtained with 94% of the theoretical density. The piezoresponse force microscopy (PFM) showed needle-shaped grains with a size of 30 nm for the samples formed at 10 MPa at both sintering temperatures. Apparently, the high temperature and high pressure used in formation reduced the energy of the band gap (
E
g
) from 3.36 to 3.09 eV. Strong emissions to 2.19, 1.86, 2.5, and 2.31 eV were obtained by exciting the samples at 325, 373, 457, and 500 nm, respectively; these emissions corresponded to blue–yellow–red regions of the visible spectrum.
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.
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