E. Dul'kin

Domain structure-dielectric property relationship in lead-free (1−x)(Bi1/2Na1/2)TiO3xBaTiO3 ceramics

The domain morphology and crystal structure of (1−x)(Bi1/2Na1/2)TiO3xBaTiO3 lead-free piezoelectric ceramics were systematically studied with transmission electron microscopy for compositions x=0.04 through 0.11. It was found that the ceramics with compositions x<0.06 display a R3c symmetry with ferroelectric domains of ∼100 nm forming complex structures at room temperature. Only nanodomains with faint contrast were observed in the compositions of 0.07≤x≤0.09. The presence of weak 1/2 (ooe) superlattice diffraction spots and absence of 1/2 (ooo) ones (o stands for odd and e stands for even miller indices) seem to suggest a P4bm symmetry at room temperature. The morphotropic phase boundary composition x=0.06 showed mixed R3c and P4bm phases. Large lamellar ferroelectric domains with P4mm symmetry were found to dominate in the ceramic of x=0.11. The observed domain structure correlates extremely well with the frequency dispersion of dielectric constant at room temperature and a new concept “relaxor antifer...

Relaxor-like behavior of BaTiO3 crystals from acoustic emission study

BaTiO3 crystals were studied by means of the acoustic emission during thermal cycling through 300–700 K range. In addition to pronounced acoustic emission at the ferroelectric phase transition temperature Tc≈400 K, also nucleation of nanoclusters was detected at somewhat smeared Burns temperature Td≈530–570 K and their local freezing at T∗≈506 K. Bias electric field shifts the T∗ and Tc linearly up, T∗ more steeply than Tc. Except for its much faster cluster dynamics than that of classical relaxor materials, BaTiO3 shows many relaxor-like features in its paraelectric phase.

Characteristic temperatures and field effect in KTa1−x NbxO3 relaxor crystals seen via acoustic emission

[100]-oriented KTa1?xNbxO3 (x=0.32) relaxor ferroelectric crystals have been studied by acoustic emission (AE) count rate in the temperature range from 200?K to 700?K. Burns temperature Td=620?K ( = 1.7??1) and intermediate temperature T*=310?K ( = 3.1??1) as well as both the tetragonal-cubic TT-C=259?K ( = 4.0??1) and orthorhombic-tetragonal TO-T=243?K ( = 5.0??1) phase transition temperatures have been clearly detected. T* is found to be influenced by an external DC electric field E:?T* essentially decreases with a slope of approximately ??60?K?cm/kV accompanied with weakening in , as E enhances. The mechanisms of abnormal T*(E) and (T) dependences are discussed.

Electric field dependence of characteristic temperatures in PbSc0.5Ta0.5O3 and Pb0.78Ba0.22Sc0.5Ta0.5O3 relaxors studied via acoustic emission

Two model relaxor ferroelectrics PbSc0.5Ta0.5O3 (undergoing a spontaneous para-to-ferroelectric phase transformation) and Pb0.78Ba0.22Sc0.5Ta0.5O3 (no long-range ferroelectric order in the absence of an external electric field) were studied by acoustic emission in the temperature range 200–600 K under a dc field E. Both compounds exhibit a para-to-antiferroelectric transformation at Tn, which is slightly above the temperature of the dielectric-permittivity maximum. For both compounds the intermediate temperature T* increases linearly with increasing E. The dT*/dE slope is larger than that of the ferroelectric transformation temperature Tc, similar to the transformation phenomena in BaTiO3. The T*(E) increase is suggested to be due to enhanced dipole polarizations inside the polar nanoregions.

Effect of A-site La, Ba, and Sr doping on the threshold field and characteristic temperatures of PbSc0.5Nb0.5O3 relaxor studied by acoustic emission

The behavior of the temperature of the dielectric-permittivity maximum Tm, the intermediate temperature T*, and the Burns temperature Td in stoichiometric PbSc0.5Nb0.5O3 (PSN) as well as in PSN heavily doped on the A-site by La (PSN-La), Ba (PSN-Ba), and Sr (PSN-Sr) was studied by means of acoustic emission (AE) under an external dc electric field (E). For all compounds, Tm exhibits a non-trivial behavior when applying E, namely, it initially decreases with the increase of E, attain a minimum at a threshold field Eth, ranging from 0.55 kV/cm for PSN to 0.25 kV/cm for PSN-Sr, and then Tm starts to increase with further increase of E. The minimum of Tm is accompanied by a pronounced maximum of the AE count rate N, which at Eth varies from 10.0 s−1 to 3.0 s−1 for all the compounds, respectively. The similarities and difference between PSN, PSN-Ba, PSN-La, and PSN-Sr with respect to Eth, the N, and the normalized AE parameter η are discussed from the viewpoint of three mechanisms: (i) chemically induced ran...

Ferroelectric precursor behavior of highly cation-ordered PbSc0.5Ta0.5O3 detected by acoustic emission: Tweed and polar nanoregions

Highly ordered ferroelectric PbSc0.5 Ta 0.5O3 crystals were studied by acoustic emission over a wide temperature range. Acoustic emission was found at three characteristic temperatures: 330, 409, and ≈600 K, which are close to those, known from the same disordered crystals, containing polar nanoregions. The microstructure in our crystals contains structural “tweed” rather than nanoregions. The coincidence of acoustic emission temperatures points towards a close structural relationship between nanoregions and “tweed.” Under electric field, these temperatures shift similar to “critical end point” behavior. The obtained data prove that acoustic emission detects signals in a wider parameter space than previously expected.

Acoustic emission during the ferroelectric transition Pm 3¯m to P4mm in BaTiO3 and the ferroelastic transition R 3¯m-C2/c in Pb3(PO4)2

Acoustic emission (AE) spectroscopy without frequency filtering (∼broadband AE) and moderate time integration is shown to be sensitive enough to allow the investigation of subtle nano-structural changes in ferroelectric BaTiO3 and ferroelastic Pb3(PO4)2. AE signals during weak phase transitions are compatible with avalanche statistics as observed previously in large-strain systems. While the data are too sparse to determine avalanche exponents, they are well suited to determine other thermodynamic parameters such as transition temperatures and critical stresses.

Acoustic Emission Study of PZN-7%PT Crystals

Phase transitions in PbZn 1/3 Nb 2/3 O 3 -7%PbTiO 3 (PZN-7%PT) relaxor ferroelectric crystals have been investigated by the acoustic emission (AE) method. Two types of transitions have been detected: (i) associated with the thermally induced (on cooling) formation of intrinsic polar nanoregions (PNRs) and (ii) related to the electric-field-induced macroscopic phase transitions. An AE signal found near 740 K corresponds to the Burns temperature, below which the PNRs begin to form. Further cooling reveals an AE signal at 500 K, which is ascribed to the shift of PNRs along their polar direction relative to the surrounding non-polar matrix in the framework of the “phase-shifted condensed soft mode” model. Monitoring of the AE response of PZN-7%PT crystals under an increasing [001] dc electric field has allowed a unique in situ observation of a sequence of phase transitions, from the zero-field rhombohedral via M A monoclinic (∼ 3 kV/cm) and M C monoclinic (∼ 16 kV/cm) to the tetragonal (∼ 19 kV/cm) phase, respectively. It is shown that AE is a very sensitive method for detecting both the PNRs kinetics and low distortion phase transitions in relaxor ferroelectrics.

Acoustic emission and dielectric studies of phase transitions within the morphotropic phase boundary of xPb(Zr1/2Ti1/2)O3-(1−x)Pb(Ni1/3Nb2/3)O3 relaxor ferroelectrics

We have carried out a combined acoustic emission (AE) and dielectric permittivity study of the xPb(Zr1/2Ti1/2)O3-(1−x)Pb(Ni1/3Nb2/3)O3 relaxor ferroelectric ceramics with compositions x=0.7–0.9 corresponding to its morphotropic phase boundary. Temperatures of all phase transitions occurring on heating are identified accurately by AE, and a direct transition between the low-temperature (rhombohedral) and high-temperature (pseudocubic) relaxor phases is found. The AE peak intensity is generally proportional to the temperature derivative of the dielectric permittivity, in agreement with a model proposed for a thermally cycled small elastic dipole.

Evidence of presence of tweed in PbSc0.5Ta0.5O3 crystals based on acoustic emission frequency spectrum analysis

Ferroelectric PbSc0.5Ta0.5O3 crystals with high degree of chemical B-site order and relaxor PbSc0.5Ta0.5O3 crystals with low degree of chemical B-site order were studied by acoustic emission near their intermediate characteristic temperature . The acoustic emission data were subjected to fast Fourier transform procedure. It was established that, while the acoustic emission spectrum amplitude of ordered PbSc0.5Ta0.5O3 exhibits a gradual monotonic decrease as frequency decreases, the one of disordered PbSc0.5Ta0.5O3 exhibits the additional features. The differences between the acoustic emission spectra are discussed in view of corresponding differences between polar nanoregions, characteristic for relaxors, and polar tweed pattern, characteristic for ferroelectrics.