J. Lajzerowicz

Nonlinear optical investigation of the bulk ferroelectric polarization in a vinylidene fluoride/trifluoroethylene copolymer

The ferroelectric polarization of vinylidene fluoride‐trifluoroethylene copolymers (70/30 mol %) is investigated using complementary measurements of the surface charge and the second harmonic intensity (at 530 nm) generated in the polymer from a Nd:YAG laser beam (at 1060 nm). Due to the nonzero electrical conductivity of the polymer (especially above room temperature), the nonlineear optical technique provides better measurement of the bulk polarization, its changes with time, the applied electric field, and temperature. First, we present optical results obtained on polarized films after removal of the electrodes: they confirm the proportionality between the second harmonic intensity and the square of the ferroelectric polarization, and the centrosymmetric character of the paraelectric phase; they also show the temperature dependence of the remanent polarization in the crystal phase. Second, we present simultaneous measurements of the surface charge and of the second harmonic intensity under very low‐frequency applied voltage through transparent electrodes. The field dependence of the measured polarization is discussed in terms of a microstructural analysis of the dielectric properties in the semicrystalline material. It is also shown that unipolar voltages applied during long periods of time are able to produce charge injection and space charge in the vicinity of the electrodes which can result in screening of the applied electric field.The ferroelectric polarization of vinylidene fluoride‐trifluoroethylene copolymers (70/30 mol %) is investigated using complementary measurements of the surface charge and the second harmonic intensity (at 530 nm) generated in the polymer from a Nd:YAG laser beam (at 1060 nm). Due to the nonzero electrical conductivity of the polymer (especially above room temperature), the nonlineear optical technique provides better measurement of the bulk polarization, its changes with time, the applied electric field, and temperature. First, we present optical results obtained on polarized films after removal of the electrodes: they confirm the proportionality between the second harmonic intensity and the square of the ferroelectric polarization, and the centrosymmetric character of the paraelectric phase; they also show the temperature dependence of the remanent polarization in the crystal phase. Second, we present simultaneous measurements of the surface charge and of the second harmonic intensity under very low‐fre...

Domain wall near a first order phase transition: role of elastic forces

Abstract We give the analytical form of the order parameter profile for a domain wall near a first order phase transition. Between the two bulk values there exists a paraelectric layer which diverges as one approaches the transition point, indicating firstly a continuous phase transition in the domain wall and secondly the non contiguity of the plus and minus domains at the transition point. The inclusion of elastic forces modifies this picture and shows that the shear modulus will induce a thermal hysteresis even in the presence of a domain wall.

Experimental Evidence for the Long‐Range Interaction of Domains in Ferroelectric KH2PO4

Detailed optical observations of domain configurations, together with simultaneous electrical measurements, have been made on ferroelectric KH2PO4. These experiments demonstrate the important variation of the dielectric constant with the lateral domain‐wall surface, and also provide evidence of the long‐range interaction between domain tips, as well as between domain tips and defects.

Switching process in twinned ferroelectric crystals

Abstract We report some characteristic examples of switching processes of the polarization in twinned ferroelectric crystals. The twinning dislocations created when the domain walls are not perfectly in twinning planes play a very important role. We note also the possible modification of the local polarization in a particular domain, near the Curie temperature.

Induced and spontaneous strain in ferroelectric ferroelastic tanane

Abstract Physical properties of the organic material tanane1 do not allow sufficiently accurate polarization measurements. As an alternative, the following order parameters were studied: spontaneous shear strain x 6, (linearly coupled to spontaneous polarization P 3), and spontaneous birefringence Δn 6, shown to be proportional to the spontaneous strain. Results of induced birefringence and strain, above and below the transition temperature (Tc = 13.5°C), are reported and discussed.

Dielectric response of the new ferroelectric: Tanane

We have studied the dielectric response of Tanane which is piezoelectric in the high-temperature phase. We report here the dielectric constant and the results of the studies of the piezoelectric resonance in the vicinity of the Curie point.

γ-ray diffractometry for the study of ferroelastic crystals: Application to KH2PO4

The shape of the rocking curves obtained by γ-ray diffractometry on KH2PC4 crystals is analysed. Perturbations near the surface [100] are shown. The applications of this technique to the study of domain switching processes are demonstrated.

Roughening transition for domain wall: Peierls force againts peierls divergence; the role of elastic energy of ferroelastic domain wall

Abstract We consider the roughening transition for domain wall and stress the important role played by the pinning to the underlying lattice. For ferroelastic domain wall the long range elastic forces suppress this transition.

Simultaneous dielectric and A.C. electrooptic measurements near the phase transition of tanane

Abstract The complex electrooptic coefficient f 63 (v, T) has been measured over a large frequency range (0.0003 Hz Tc ). A critical dispersion has been observed at very low frequency, and is attributed to static defects or mechanical imperfections. In the vicinity of Tc . simultaneous measurements of the dielectric constant e33 (1500 Hz) and the electrooptic coefficient. f 63 (1500 Hz) show that they are linearly coupled by a temperature independent coefficient which is not affected by the dispersion.

Unified presentation of four fundamental inequalities

We suggest an unified presentation to teach fundamental constants to graduate students, by introducing four lower limits to observed phenomena. The reduced Planck constant