V. Zauls

Novel second-order nonlinear optical polymer materials containing indandione derivativatives as a chromophore

Second order non linear optical (NLO) properties of sPMMA based host-guest systems containing eight dimethylaminobenzylidene -1, 3 - indandione (DMABI) related chromophores have been investigated by means of quantum chemical calculations and SHG experimental characterization. Ab initio calculations with basis set 6-31G were used for molecular geometry determination as well as in the calculations of molecular hyperpolarizability by FF approach. Influence of the chromophore concentration on the host-guest film NLO performance was obtained by SHG Maker fringe experiments. The highest value of d53233 =80 pm/V (frequency corrected value d033 =12 pm/V) at chromophore concentration 15 %wt have been recorded for tret-butyl substituted DMABI chromophore.

Effects of structure ordering, structure defects and external conditions on properties of complex ferroelectric perovskites

Abstract Structural rearrangements in lead-containing (A‘A’) (B’B“)O3 type perovskite compounds are caused by technological treatment, high-energy radiation and ambient conditions. Variation of structure ordering along with modification (substituted or defected solid solutions) may provide promising compositions for applications, e.g., cascade microcryogenic devices (PST solid solutions); efficient piezoelectric materials – here the new (1 – x)Pb(Lu1/2Nb1/2)O3 – xPbTiO3 system in the morphotropic region. The maximum values of the electromechanical coupling coefficients kp = 0·663, kt = 0·481, k 31 = 0·355 were attained in compositions PLuNT 59/41 (Tm = 353°C) near the morphotropic phase boundary. In P(L)ZT and PLT thin films asymmetry of piezoelectric coefficient d 33 hysteresis diminished values of d 33 and their frequency dependence were attributed to residual stress at the film-substrate/electrode interfaces and unrelaxed strain characteristic in highly oriented thin films. Neutron irradiation by fluen...

Dynamics of Polar Clusters in PMN Ceramics: Comparison with PMN Single Crystal

The dielectric permittivity of PMN ceramics was measured in the frequency range from 20 Hz to 37 GHz. From the frequency dependence of the real and imaginary parts of dielectric permittivity, the distribution of relaxation times f(τ) was calculated. The f(τ) function broadens significantly, and the second maximum appears below the 270 K temperature. The dielectric response and also relaxation time distribution of PMN ceramics was compared with the previous results of PMN single crystal. The results showed that dynamics of polar nano regions in PMN ceramics is suppressed due to the small size of grains in the ceramics.

PHASE TRANSITIONS AND PROPERTIES OF PEROVSKITE FERROELECTRIC CERAMICS AND FILMS FOR CERTAIN APPLICATIONS

Abstract The structure-properties relationships and phase transitions in perovskite ceramics, and films of PLZT, PLZST, PST, PSN, PMNT compounds are discussed with regard to ordering, relaxor behaviour, pronounced ferroelectric, electromechanical and electrocaloric properties. The theoretical approach is extended to the time dependent Ginsburg-Landau model. The evolution of dielectric properties in relaxors after the change of temperature and electric field creating an increase of dielectric permittivity is found to follow a logarithmic law of decay. A strong electromechanical response is observed in a number of thin films of different compositions.

Antiferroelectric PbZrO3 thin films: structure, properties and irradiation effects

Abstract Irradiation effects on highly oriented antiferroelectric PbZrO 3 and ferroelectric Pb 0.92 La 0.08 (Zr 0.65 Ti 0.35 )O 3 thin films are investigated being exposed to neutron irradiation up to fluence 2*10 22 m −2 . The higher resistance of antiferroelectric PbZrO 3 thin films as compared to ferroelectric heterostructures to large fluences of neutron irradiation is recognized and discussed. Influence of two factors (structural and charge) was taken into account analysing irradiation effects on materials of different polarization states: ferroelectric PLZT (ceramics and thin films) and antiferroelectric PbZrO 3 films.

Formation of Optical Gradient in Chemical Solution-Derived PbZr0.52Ti0.48O3 Thin Films: Spectroscopic Ellipsometry Investigation

Investigation using a variable angle spectroscopic ellipsometer revealed the influence of sample preparation conditions on sol-gel PbZr 0.52 Ti 0.48 O 3 (PZT 52/48) thin-film homogeneity that allows identification and further optimization of thin-film performance. Separate crystallization of the layers determined the optical gradient appearance, irrespective of the chemical solvents used in this work. A more refined analysis showed that a refractive index gradient was apparent in the samples in which lattice parameters strongly changed with thickness. For these films, energy-dispersive X-ray spectroscopy analysis showed significant variation in Pb and Zr. Additionally, complex dielectric functions for each PZT 52/48 thin film in the wide phonon energy (1.03-5.39 eV) range were evaluated.

Linear and nonlinear optical properties of Langmuir–Blodgett multilayers from chromophore-containing maleic acid anhydride polymers

Abstract Organized polymer films prepared from amphiphilic side-chain polymers were investigated with respect to their application in passive or active photonic devices. The polymers were synthesized by means of polymer analogous reaction of azo chromophores with a maleic acid anhydride polymer which bears saturated hydrophobic side chains. The resulting polymer contains, besides hydrophilic groups and hydrophobic side chains, azo chromophores with high second-order hyperpolarizability which are attached to the main chain via a spacer. In order to increase the hydrophobic character of the chromophore, a fluorinated moiety was chosen as acceptor of the chromophore. Langmuir–Blodgett (LB) technique was applied for preparation of multilayer structures with distinct supramolecular architecture from these polymers. They are characterized by high anisotropy and a special combination of linear and nonlinear optical (NLO) properties. The polymers were deposited both in Y-type and Z-type LB layers. The Y-type layers of the azopolymer show high birefringence and dichroism but small nonlinear response which originates from the first deposited layer only. Multilayers of the azopolymer deposited in Y-type configuration are characterized by high internal order which can be concluded from a pronounced Bragg-peak and Kiessig-fringe patterns as obtained from gracing incidence X-ray scattering. Experiments to deposit the active polymer directly in Z-type configuration by passing a blank water compartment before layer deposition in a double compartment LB-trough led to the result that well-ordered, anisotropic films are obtained only if the number of deposited monolayers is limited to a value of about 30. The layers deposited in Z-type manner show low order. This can be concluded from the fact that only a weak Bragg-peak is observed in the X-ray scattering curves, and Kiessig-fringes are very weak or missing. The same conclusion can be drawn from ellipsometric and second-harmonic generation (SHG) experiments. A second kind of Z-type multilayers was prepared by alternate deposition of the active azopolymer and of another maleic acid anhydride polymer without chromophores. They show similar linear optical properties like Y-type layers but due to the noncentrosymmetric internal structure, a NLO second-order response grows proportional to the square of the sample thickness. Again, thick layers of the azopolymer prepared by alternate deposition LB-technique were prepared, which can be used as active waveguide for second-order NLO application.

New chromophores and polymers for second-order nonlinear optics

Linear conjugated, fluorine-containing chromophores are differing from conventional chromophores like disperse red one by a reduced linear refractive index. Second order nonlinear optical susceptibilities of asymmetrically substituted fluorine-containing dyes reach, however, values as high as those of DR I or of similar chromophores. This can be concluded from measurements of solvatochromy of absorption and fluorescence spectra, electroabsorption measurements, and from quantum chemical calculations carried out for a series of azomethine and azo dyes. The chemical constitution of the conjugated part of investigate chromophores has an important influence both on linear and non nonlinear optical properties. So azomethine dyes show a blue shifted absorption in comparison to the absorption of azo chromophores. This goes along with lower off-resonant second order susceptibility. Introduction of fluorine into the acceptor part of the molecule by attaching a CF3- group does not lead to a significantly lower second order susceptibly in comparison to non-fluorinated chromophores. Perfluorination of the acceptor part result in case of the investigated molecules in an increased second order susceptibility as compared to the non-fluorinated chromophore. Polymers which contain these chromophores are either prepared by physical doping or by covalent bonding of the dyes to the polymeric main chain.In case of physically doped polymers the classes of thermally stable allylic polymers and of polyphenyl quinoxalines (PPQs) were used as matrix material. These polymers show miscibility with the investigated chromophores up to high concentrations and are haracterized by glass transition temperatures between 140 degrees C and 180 degrees C or 180 degrees C and 350 degrees C (PPQs) dependent on chemical structure and on dye concentration. Polymers which contain the active chromophores in side chains were prepared on basis of maleic acid anhydride or as novolak epoxy amine aduct polymer. The former can be utilized for preparation of waveguides by means of Langmuir-Blodgett technique while the later provide films of excellent quality by spin-coating and subsequent corona poling. Second order susceptibilities of the polymer films as determined by second harmonic generation reach values between 5 and 27 pm/V dependent on chromophore concentration and preparation conditions.

Laser-induced selftransparency in PLZT ceramics

Abstract We report measurements of selftransparency effects in PLZT 8/65/35 ceramics for various wavelength of laser radiation λ = 0. 5+6 νm. The results are interpreted in terms of thermally induced phase transitions, thermal lens and photorefraction in PLZT. Optimal conditions for the light-by-light control in PLZT 8/65/35 are achieved and discussed.

SINTERING OF LEAD-FREE (K0.5Na0.5)NbO3 BASED SOLID SOLUTION

ABSTRACT In this study lead-free solid solution (K0.5Na0.5)NbO3 was prepared, structure, dielectric parameters of ceramics were investigated. The doping of sintering aids did not affect the crystallographic structure of the ceramics significantly; all ceramic samples had a single-phase perovskite structure. Added elements CdO, ZnO, MnO2, V2O5 effectively decreased the sintering temperature of KNN by 50°–80°C. All sintering aids influenced sinterability, microstructure and dielectric properties of ceramics. Dielectric constant for doped samples increased from 6000 up to 8000; Pr = 15 μC/cm2, Ec = 9 kV/cm, d33 = 110 pC/N, kp = 0.38 and Qm = 190 for MnO2 doped samples.