Hichem Dammak

Origin of the Giant Piezoelectric Properties in the [001] Domain Engineered Relaxor Single Crystals

Relaxor single crystals PZN–9%PT have been cut and poled along [101] direction for which the spontaneous polarization Ps is approximately parallel to the poling field Ep. The piezoelectric matrix of the monoclinic single-domain (1M state) has been determined, in the approximation of an orthorhombic symmetry. The shear mode (15) along [101], gives the highest electromechanical coupling factor k15 (>80%) and the largest piezoelectric coefficient d15 (~3200 pC/N). The properties of the disoriented 1M state have been calculated from a change of axes. The maximum of d33θ is obtained along a direction close to [001]. This is due to the very large value of d15 compared to d33 in the basic 1M state. On the other hand the transverse piezoelectric coefficient along [uv0] for the [001] disoriented Ps single domain presents a strong anisotropy. Finally, in the [001] domain engineered configuration, an important extrinsic contribution of the domain coexistence is evidenced by comparing calculated and measured coefficients.

Domain Structures in Monoclinic Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 Poled Single Crystals

A tetragonal (T) ?monoclinic (M) phase transition characterized by a wide thermal hysteresis is observed in Pb(Zn1/3Nb2/3)O3?PbTiO3 (PZN?PT) single crystals close to the morphotropic composition PZN?9%PT. The domain structure of crystals, determined by X-ray diffraction and optical observations, is dependent on the poling crystallographic direction. A monoclinic quasi-single domain structure is obtained by poling along the pseudocubic [101] direction whereas an unexpected monoclinic multidomain state with macroscopic 2 mm symmetry can be obtained for [001] poled crystals. Finally it is shown that the largest piezoelectric response corresponds to the monoclinic multidomain state of [001] poled crystals.

Electric-field-induced orthorhombic phase in Pb[(Zn1∕3Nb2∕3)0.955Ti0.045]O3 single crystals

The ferroelectric phase transitions of [1¯01]-, [001]-, and [111]-oriented Pb[Zn1∕3Nb2∕3]O3–4.5%PbTiO3 (PZN–4.5%PT) single crystals were investigated as a function of temperature (T between 300 and 450K), and electric field (E field between 0 and 300kV∕m) by dielectric and x-ray diffraction combined measurements. Under null E field, PZN–4.5%PT exhibits the following phase transitions: cubic (C)→tetragonal (T)→rhombohedral (R), during cooling. Under E field applied on a [1¯01]-oriented single crystal, an intermediate orthorhombic (O) ferroelectric phase is induced at temperatures intermediate between that of the T and R phases. The temperature range of existence of this O phase depends both on the crystal orientation and on the measurement conditions: field cooling (FC), zero-field heating after field cooling (ZFHAFC), or field heating (FH). When E field is applied along [1¯01], the stability range is within 40K in FC and only 15K in ZFHAFC; when E field is applied along [001] or [111], this range is still...

The cubic-to-rhombohedral phase transition of Pb(Zn1/3Nb2/3)O3: a high-resolution x-ray diffraction study on single crystals

The cubic-to-rhombohedral (C–R) phase transition of the ferroelectric relaxor Pb(Zn1/3Nb2/3O3) is investigated by means of a high-resolution x-ray diffraction study on single crystals. The phase transition is diffuse and spreads over the temperature range TCR = 385 ± 5 K to TR = 325 ± 5 K. Below TCR, the cubic phase transforms progressively into rhombohedral domains whose average size, about 60–70 nm in the [111] direction, remains unchanged as temperature is lowered, so no growth of the R-domains is observed. At TR, the nanometric R-domains fully pave the crystal but structural mismatches between adjacent domains generate stresses, which increase as temperature is lowered. The anomalous broadening of diffraction peaks of the R-phase, which originates from size and strain effects, can be suppressed by applying a dc electric field, along the [111] direction, which transforms the polydomain state into a rhombohedral quasi-monodomain state.

Full tensorial characterization of PZN-12%PT single crystal by resonant ultrasound spectroscopy

An experimental setup based on the electrical excitation of a piezoelectric sample is proposed for resonant ultrasound spectroscopy measurements. The detection of the mechanical vibrations is performed by means of a laser interferometer. At the same time, the free vibrations of piezoelectric parallelepipeds of tetragonal and hexagonal symmetries are modeled taking into account the effect of the sample metalization. The paper presents the full elastic, piezoelectric and dielectric tensors of two PMN-34.5%PT ceramic and PZN-12%PT single crystal cubes.

Orientation Distribution and Fiber Texture of Highly Oriented Piezoceramics: (1-x)PbMg1/3Nb2/3O3–xPbTiO3 System

Textured (1-x)PbMg1/3Nb2/3–xPbTiO3, (PMN–xPT), ceramics were synthesised by the homo template grain growth (HTGG) technique using PMN–PT nanoparticles and cubic single crystals seeds (templates). The orientation of the templates was obtained during tape casting. Sintering was performed under controlled O2/PbO partial pressure. The fraction of textured ceramics was estimated by the Lotgering method at RT and above Tc. Textured tape cast ceramics display a quasi complete (001) texture ( f=0.99) in the cubic phase. The (011) pole figure reveals a (001) fibre texture in accordance with the optical observation. The texture was obtained in all volumes of ceramics and only a small orientation distribution was observed (<6°).

2T domain-engineered piezoelectric single crystals: Calculations and application to PZN–12%PT poled along [101]

This work is devoted to a study of the [101] domain-engineered PZN–12%PT single crystals. The full electromechanical tensor of PZN–12%PT in its tetragonal single domain state 1T is determined by the resonance method and used as input data. Observations of the domain structure of the [101]-poled 2T crystals by polarized light microscopy reveal a laminar structure consisting of thin layers stacked along the macroscopic polarization direction. We give analytical expressions for effective constants of this laminate multidomain pattern, taking into account the clamping effect resulting from domain coexistence. The calculated effective properties are found in good agreement with the experiments within experimental uncertainties. It is found that domain coexistence affects primarily the transverse dielectric constants e11 and e22. This effect is related to the emergence of internal shear stresses and depolarizing electric fields that are most significantly driven by the shear piezoelectric constant d15 and diele...

Size-dependent infrared properties of MgO nanoparticles with evidence of screening effect

We have investigated the infrared (IR) absorption properties of MgO nanoparticles (NPs) with the means of molecular dynamics simulations. Several size effects have been observed. We show in particular that the absorption of IR radiation does not occur predominantly through the polariton mode but preferentially through surface modes. This enhanced surface absorption is found to result from the absence of dielectric screening of the first atomic layer of the NPs. We demonstrate concomitantly that a macroscopic description of electrodynamics is inadequate to capture these unusual IR properties.

TEM OBSERVATIONS OF IRON AND NICKEL FOILS IRRADIATED BY MEV FULLERENES AT ROOM TEMPERATURE

Abstract It is shown that a new specific effect takes place in iron during irradiation with ∼10 MeV fullerene beams. A dislocation line with various shapes is observed in the close vicinity of the projectile path leading to a strain field confined inside a 20–40 nm diameter “cylinder”. Similarly to previous observations in titanium and zirconium (Dammak et al., Phys. Rev. Lett. 74 (1995) 1135), this effect might be due to the strong localisation of the energy deposited during the projectile slowing-down process. However no damage is observable in nickel irradiated in the same conditions. These results should be explained by the previously established relation between the sensitivity of a metal to a high rate of energy deposition in electronic excitations and the existence of a high pressure phase in the pressure-temperature phase diagram (Dammak et al., Nucl. Instr. and Meth. B 107 (1996) 204).

Zero-Point Energy Leakage in Quantum Thermal Bath Molecular Dynamics Simulations

The quantum thermal bath (QTB) has been presented as an alternative to path-integral-based methods to introduce nuclear quantum effects in molecular dynamics simulations. The method has proved to be efficient, yielding accurate results for various systems. However, the QTB method is prone to zero-point energy leakage (ZPEL) in highly anharmonic systems. This is a well-known problem in methods based on classical trajectories where part of the energy of the high-frequency modes is transferred to the low-frequency modes leading to a wrong energy distribution. In some cases, the ZPEL can have dramatic consequences on the properties of the system. Thus, we investigate the ZPEL by testing the QTB method on selected systems with increasing complexity in order to study the conditions and the parameters that influence the leakage. We also analyze the consequences of the ZPEL on the structural and vibrational properties of the system. We find that the leakage is particularly dependent on the damping coefficient and that increasing its value can reduce and, in some cases, completely remove the ZPEL. When using sufficiently high values for the damping coefficient, the expected energy distribution among the vibrational modes is ensured. In this case, the QTB method gives very encouraging results. In particular, the structural properties are well-reproduced. The dynamical properties should be regarded with caution although valuable information can still be extracted from the vibrational spectrum, even for large values of the damping term.