M. M. Neradovskiy

Formation of dendrite domain structures in stoichiometric lithium niobate at elevated temperatures

Formation of the dendrite-type self-organized domain structures during polarization reversal at elevated temperatures (above 230 °C) has been revealed and studied in stoichiometric lithium niobate LiNbO3 single crystals. Optical, confocal Raman, scanning electron, and piezoelectric force microscopy have been used for domain visualization. It has been shown experimentally that formation of the dendrite-like structures has been attributed to correlated nucleation caused by a field distribution in the vicinity of the charged domain walls.

Nanodomain structures formation during polarization reversal in uniform electric field in strontium barium niobate single crystals

We have studied the ferroelectric nanodomain formation in single crystals of strontium barium niobate Sr0.61Ba0.39Nb2O6 using piezoelectric force microscopy and Raman confocal microscopy. The nanodomain structures have been created by application of the uniform electric field at room temperature. Four variants of nanodomain structure formation have been revealed: (1) discrete switching, (2) incomplete domain merging, (3) spontaneous backswitching, and (4) enlarging of nanodomain ensembles. Kinetics of the observed micro- and nanodomain structures has been explained on the basis of approach developed for lithium niobate and lithium tantalate crystals.

Periodic domain patterning by electron beam of proton exchanged waveguides in lithium niobate

Formation of domain structure by electron beam irradiation in congruent lithium niobate covered by surface dielectric layer with planar and channel waveguides produced by Soft Proton Exchange (SPE) process has been studied. Formation of domains with arbitrary shapes as a result of discrete switching has been revealed. The fact was attributed to ineffective screening of depolarization field in the crystals with a surface layer modified by SPE process. The dependences of the domain sizes on the dose and the distance between irradiated areas have been revealed. Finally, we have demonstrated that electron beam irradiation of lithium niobate crystals with surface resist layer can produce high quality periodical domain patterns after channel waveguide fabrication. Second harmonic generation with normalized nonlinear conversion efficiency up to 48%/(W cm2) has been achieved in such waveguides.

Domain structures and local switching in lead-free piezoceramics Ba0.85Ca0.15Ti0.90Zr0.10O3

Lead-free piezoelectrics are becoming increasingly important in view of environmental problems of currently used lead-based perovskites such as lead zirconate titanate (PZT). One of the recent candidates for PZT replacement, solid solutions of BaZr0.2Ti0.8O3 and Ba0.7Ca0.3TiO3, are investigated in this work by piezoresponse force microscopy. Coexistence of the tetragonal and rhombohedral phases in this material is observed, which probably gives rise to easy polarization switching due to multiple domain states. The period of observed domain lamella scales with the grain size obeying well-known square root dependence characteristic of BaTiO3 ceramics. Domain switching and relaxation are investigated at the nanoscale as a function of the applied voltage and duration of the applied voltage pulses. The observed distortion of piezoresponse hysteresis loops near grain boundaries is attested to the increased concentration of defects. Nanoscale piezoelectric properties of these materials are discussed.

Domain switching by electron beam irradiation of Z+-polar surface in Mg-doped lithium niobate

The appearance of the static domains with depth above 200 μm in the bulk of MgO-doped lithium niobate single crystals as a result of focused electron beam irradiation of Z+-polar surface was demonstrated. The created domain patterns were visualized by high-resolution methods including piezoresponse force microscopy, scanning electron microscopy, and confocal Raman microscopy. The main stages of the domain structure formation were revealed and explained in terms of the original model.

Domain Kinetics in Lithium Niobate Single Crystals with Photoresist Dielectric Layer

The influence of the artificial surface layer (photoresist film) on the domain kinetics was studied in congruent lithium niobate single crystals. The switching current data was fitted by modified Kolmogorov-Avrami formula. The qualitative change of the domain structure evolution for photoresist film thickness above 2 μm was revealed by in situ optical visualization and analysis of the switching current data. The linear dependence of the threshold field increase on the film thickness was found. The quasi-regular nanodomain structures on Z+ polar surface were studied by scanning probe and Raman confocal microscopy and the domain evolution scenario was revealed.

Micro-Raman Visualization of Domain Structure in Strontium Barium Niobate Single Crystals

Raman confocal microscopy was applied for visualization of the ferroelectric domain structure in strontium barium niobate single crystals. The studied domain structure was produced by electric field poling of the single domain state at room temperature. Essential frequency shift of the certain Raman band in the vicinity of domain walls was revealed. Recording of this parameter during two-dimensional scanning was used for reconstruction of the domain images both at the surface and in the bulk.

Water Effect on Proton Exchange of X-cut Lithium Niobate in the Melt of Benzoic Acid

The influence of controllable amount of water admixture (up to 0.5 w.%) in benzoic acid on the proton exchange process of X-cut congruent lithium niobate was studied in this paper by means of mode spectroscopy, optical microscopy, optical profilometry, atomic force microscopy, XRD, and chemical etching. It has been determined that addition of 0.5 w.% Н2О to benzoic acid increases proton exchange rate and changes phase composition and number of defects of proton exchanged layer in lithium niobate.

Energy harvesting from nanofibers of hybrid organic ferroelectric dabcoHReO4

We report excellent piezoelectric and pyroelectric properties of electrospun nanofibers based on the hybrid ferroelectric 1,4-diazabicyclo[2.2.2]octane perrhenate (dabcoHReO4). Ferroelectric nanoparticles are embedded into the fibers being naturally aligned with the major polarization component along the fiber axis. A flexible piezoelectric nanogenerator consisting of an aligned array of dabcoHReO4 fibers provides a voltage above 100 mV under a moderate strain level. The pyroelectric coefficient in as-electrospun dabcoHReO4 fiber mat is similar to that in poled polyvinylidene difluoride nanofibers. The results show that the nanofibers based on dabcoHReO4 have a great potential for pyroelectric and piezoelectric autonomous energy harvesting with natural advantages such as biocompatibility, flexibility, low cost, and easy fabrication.

Effect of surface disorder on the domain structure of PLZT ceramics

ABSTRACT Pb1-xLax(Zr0.65Ti0.35)1-x/4O3 (PLZT x/65/35) ceramics were studied by Piezoresponse Force Microscopy in order to understand the origin of domain structure as a function of La content. We show that the domain topology is mainly determined by the composition and grain size. The characteristic correlation length decreases with increasing La content, being sensitive also to the synthesis method. The behavior of the correlation length is linked to the macroscopic properties, showing a strong increase of disorder with La doping. The roughness exponent for the domain wall in PLZT 9/65/35 is close to 2/3 indicating 1D character of domain walls in relaxors.