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«ANNUAL REPORT Riga 2012 Annual Report 2011, Institute of Solid State Physics, University of Latvia. Editor: A.Krumins. Composed matter: A.Muratova. ...»

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X-ray diffraction analysis of the (1-x)(K0.5Na0.5)Nb0.96Sb0.04O3-xBaTiO3 (x=0.01, 0.015, 0.02) (KNNS-xBT) ceramics confirmed single phase perovskite structure with monoclinic or tetragonal cell depending on x. No peak corresponding to the secondary phase was observed implying that KNNS and BT ceramics formed homogeneous solid solution.

The fracture microstructure of the (1-x)(K0.5Na0.5)Nb0..96Sb0.04O3-xBaTiO3 (x=0.01, 0.015, 0.02) was investigated by SEM as shown in Figs. 1. a-c.

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With increasing BaTiO3 concentration in the composition the average grain sizes decrease; the shape of grains is rectangular although a little rounded. The fracture occurs along the grain boundaries except for the samples with x=0.01. A little amount of liquid phase is also detected. The EDS made in the chosen microregions of the sample surface analysis confirmed the purity and experimentally assumed qualitative composition. The obtained socalled “mappings” with EPMA revealed quite even distribution of elements on the polycrystalline material surface and at the same time confirmed the qualitative composition of examined samples.

1,1

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7500 1,5 5000 1,0 2500 0,5

–  –  –

K. Bormanis, A.I. Burkhanov*, S.V. Mednikov**, and Liu Thi Njan** The dielectric nonlinearity in Sr0.75Ba0.25Nb2O6 (SBN-75) ceramics is observed. Earlier studies of polarisation switching in SBN-75 single crystals [1, 2] had shown essential decrease (as compared with ordinary ferroelectrics) of polarisation with each cycle in the thermal range of the relaxor phase, which had been related to “freezing” processes in disordered ferroelectrics.

Manifestations of similar processes were of interest in SBN-75 ceramics taking into account that dielectric permittivity ε’ and dielectric loss ε” are smaller compared with single crystal by more than order of magnitude if measured along the polar axis.

Figure 1. Field dependence of dielectric permittivity at different temperatures for SBN-75.

Behaviour of reverse ε′ (Е=) at T Tm and at T ≥ Tm in SBN-75 ceramics is presented in Fig. 1. a and b, respectively. Behaviour of dielectric nonlinearity at T Tm, different from single crystal, is similar to that of ordinary ferroelectrics – the ε′(Е=) curve is closed while at T ≥ Tm the magnitude of ε′ practically does not depend on the bias field Е=.

Possible effects of mechanical tension on features of dielectric nonlinearity in ceramics are discussed, suppression of relaxor properties in case of ceramic materials, in particular.

References [1] A.I. Burkhanov, A.V. Shil′nikov, and R.E. Uzakov. Crystallography, 1997, 42, 1069.

[2] V.V. Gladky, V.A. Kirikov, E.V. Pronina, T.R. Volk, R. Pancrat, M. Vëleke. Solid State Physics, 2001, 43, 2052.

* Volgograd State Architectural and Engineering University.

** Volgograd State Technical University.

THERMAL EXPANSION AND ELECTROMECHANICAL PROPERTIES IN

Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 SOLID SOLUTIONS M. Dunce, E. Birks, I. Aulika*, A. Fuith**, M. Antonova, R. Taukulis, and A. Sternberg The transfer from diffused to normal ferroelectric phase transition, passing different stages of relaxor behaviour, was found in Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 by research of polarization and dielectric properties. Here thermal expansion and electromechanical properties are studied for these compositions.

Two methods were used in the studies of electric field-induced deformation - the classical resonance-antiresonance method, was used to determine piezoelectric coefficients for compositions, which are in FE state at room temperature. Whereas Michelson interferometer with an original method of interference analysis was used for measurements of electric field-induced deformation in quasistatic regime. The character of the obtained polarization dependence of the deformation corresponds to the place of the concrete composition in the phase diagram. It was stated that for compositions, which are in the relaxor state at room temperature, the deformation is proportional to polarization square, which allows us to determine values of electrostriction coefficient Q11. The largest electric fieldinduced deformation of 0.054% was observed for composition NBT-ST-PT 0.4/0.52/0.08, which is close to morphotropic phase boundary between pseudocubic and tetragonal structure.

Studies of thermal expansion were used for characterization of the relaxor state. Thus attention was paid to determination of the Burns temperature (TB), using measurements of thermal expansion. The measurements did not give us possibility to determine TB precisely only from temperature dependence of the thermal expansion. However comparing NBT-STPT compositions with different character of the relaxation state allowed us to establish that all of these compositions have similar values of the thermal expansion coefficient at T400oC.

From this we can conclude that in the mentioned temperature range the thermal expansion does not depend on local polarization, which is different for these compositions, and define TB~400oC.

* Italian Institute of Technology-IIT@PoliTO, Italy.

** University of Vienna, Functional Materials, Austria.

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M. Dunce, E. Birks, M. Antonova, M. Kundzinsh, A. Sternberg, and M. Livinsh The dielectric nonlinearity is studied in ferroelectric relaxors 0.92PbMg1/3Nb2/3O3PbTiO3 (PMN-PT) 0.4Na1/2Bi1/2TiO3-0.5SrTiO3-0.1PbTiO3 (NBT-ST-PT) and Pb0.9075La0.0925(Zr0.65Ti0.35)0.9775O3 (PLZT). It is shown that above the temperature of dielectric permittivity maximum nonlinearity of dielectric permittivity corresponds to electric field dependence of polarization.

Decreasing of dielectric permittivity under DC electric field, characteristic for relaxors, is found in PMN-PT and NBT-ST-PT. Dependence of the distribution function of relaxation times, used for description of dielectric dispersion, is weakly influenced by electric field. A parallel shift of dielectric permittivity is observed in all frequency range, where dielectric dispersion exists. It is showed that the approach, usually used for description of P(E), does not correspond to the temperature dependence of dielectric permittivity. It is not confirmed that distribution of size of PNR is a reason for distribution of relaxation times.

Low nonlinearity coexists with expressed dielectric dispersion in PLZT. The nature of nonlinearity and characteristic bending of P(E) in this composition are explained by existence of internal bias field, caused by presence of Me3+ and oxygen vacancy defect dipole.

ELECTROCALORIC EFFECT IN Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 SOLID SOLUTIONS

J. Hagberg*, M. Dunce, E. Birks, M. Antonova, and A. Sternberg Previously a gradual transfer from relaxor to ferroelectric state in dependence on concentration of constituents, passing different stages of relaxor behaviour, was established in triple solid solutions (1-x-y)Na1/2Bi1/2TiO3-xSrTiO3-yPbTiO3 ((1-x-y)NBT-xST-yPT) by research of dielectric properties. The electric-field-induced first-order phase transition, characterized by double hysteresis loops, is found in a certain range of the compositions.

In this work the electrocaloric effect is studied in the solid solutions NBT-ST-PT in the concentration range of relaxor ferroelectric properties. The temperature and electric field dependences of the electrocaloric effect qualitatively correspond to the results, established earlier in other relaxor ferroelectrics.

High values of the electrocaloric effect are found at the electric-field-induced phase transition in the composition range, where the relaxor properties diminish in favour of the ferroelectric state. In compositions 0.4NBT-0.4ST-0.2PT and 0.4NBT-0.35ST-0.25PT these values reach ~1.1 oC at E=20 kV/cm in the region of the phase transition. Very different nature of ECE is found in compositions with low concentration of PT, where ferroelectric state can not be reached even under electric field. It was showed that the calculation of ECE in relaxor state according to traditional thermodynamic considerations does not correspond to the experimental results.

* University of Oulu, Finland.

PRINCIPLES OF DESIGNING CONTAINERS FOR THERMO-CHEMICAL

TREATMENT OF HIGH PURITY COMPOUNDS

–  –  –

Mathematical modelling of the distribution of strain in layered quartz ceramics with protective coating of niobium pentoxide from two sides is tested. It is found that fragmentation of the basic layer (decreasing the area of the continuous boarder between layers) and smoothing of sharp edges of the base fragments should reduce the strains on the boundary between the substrate and coating and, correspondingly, enhance the thermal resistance of the samples.

Treatment of the niobium pentoxide coating by concentrated light flow (CLF) induces a network of fractal micro- and nano-size fractures that compensates the difference of thermal expansion between the layers. The absolute value of the negative coefficient of linear thermal expansion (CLTE) of Nb2O5 treated by CLF decreases while the curve of relative thermal expansion becomes more symmetric. Due to the fractal micro- and nano-size structures forming at treatment by CLF in optical oven the CLTE of tantalum pentoxide samples exhibits a region of negative or close to zero values. The fraction of nanometre-size fractures in case of Ta2O5 treatment by CLF is likely considerably larger as compared with Nb2O5.

The studies have demonstrated that possible control of bulk expansion of the material and fragmentation of the basic layer allow to obtain layered ceramics and products thereof possessing enhanced thermal resistance to withstand thermal cycling.

Experimental acoustic emission studies have confirmed the increase of thermal resistance of the samples by factor ~1.5. Smoothing the edges of the fragments of the ceramic substrate provides additional increase of thermal resistance by ≈15 %. Containers for calcination of high purity grade niobium hydroxide made of fragmented ceramic substrate and coated by CLF-processed Nb2O5 have shown improved thermal resistance. Such containers, as shown in figure, withstand thousands of fast thermal cycles Troom ↔ 1000 ºC.

Figure. Container of structured quartz core and niobium pentaoxide coating: a – rounded corners, b – seams connecting segments (c) of quartz ceramics, d – protective coating of niobium pentaoxide.

* Institute of Chemistry, Kola Science Centre RAS, Apatity, Murmansk Region, Russia.

** Frantsevich Institute for Problems of Materials Science of NASU.

DIELECTRIC PROPERTIES AND CONDUCTIVITY OF FERROELECTRIC

Li0.07Na0.93Ta0.1Nb0.9O3 and Li0.07Na0.93Ta0.111Nb0.889O3 SOLID SOLUTIONS K. Bormanis, M.N. Palatnikov*, V.V. Efremov*, N.V. Sidorov*, and I.N. Efremov* The ABO3 ferroelectric (FE) solid solutions (SS) of perovskite structure on the basis of sodium niobate exhibit a number of properties interesting for application: relatively low values of density and dielectric permittivity, high ultrasonic velocity and good piezoelectric performance, and a wide range of mechanical Q-factor. Results of dielectric and conductance studies over the thermal range of 290 – 700 K and frequency range of 25 - 106 Hz in Li0.07Na0.93Ta0.1Nb0.9O3 and Li0.07Na0.93Ta0.111Nb0.889O3 perovskite FESS are discussed.

Electric properties and phase transition parameters of Li0.07Na0.93Ta0.1Nb0.9O3 and Li0.07Na0.93Ta0.111Nb0.889O3 FESS are found to depend substantially on the way the initial mixture is synthesised. A first-order FE phase transition proceeds in the Li0.07Na0.93Ta0.1Nb0.9O3 and Li0.07Na0.93Ta0.111Nb0.889O3 FESS within the observed range of temperature. The co-precipitated Ta2yNb2(1-y)O5 pentoxides being used for synthesis of the Li0.07Na0.93Ta0.111Nb0.889O3 FESS it is possible to achieve rather high values of dielectric permittivity at high frequencies while the Curie point shifts by ~ 75 K to a lower temperature as compared with Li0.07Na0.93Ta0.1Nb0.9O3, synthesised from mechanical mixture of the Ta2O5 and Nb2O5 oxides, which cannot be explained by the minor difference in proportions of the ingredients in the final SS. Techniques of obtaining the initial oxides has also a substantial effect on the ion conductivity of the Li0.07Na0.93Ta0.1Nb0.9O3 and Li0.07Na0.93Ta0.111Nb0.889O3 FESS. The activation energy of ion conductivity in the Li0.07Na0.93Ta0.111Nb0.889O3 FESS is lower while its value – considerably higher compared with Li0.07Na0.93Ta0.1Nb0.9O3. The different thermal behaviour of the real part of dielectric permittivity and conductivity between the Li0.07Na0.93Ta0.1Nb0.9O3 and the Li0.07Na0.93Ta0.111Nb0.889O3 FESS are obviously related to the way of obtaining the initial oxides Ta2O5 - Nb2O5 and Ta2yNb2(1-y)O5.

* I.V. Tananaev Institute of Chemistry, Kola Science Centre RAS, Apatity, Russia.

–  –  –

V. Karitans, M. Ozolinsh, S. Fomins, A. Svede, G. Krumina, and N.G. Iroshnikov** Lower-order and higher-order ocular aberrations influence not only visual perception but also appearance of retinal images. We suggest that apparent diameter of blood vessels may differ for various types of aberrations based on how the maps of point spread functions are orientated to these vessels. We test our hypothesis by simulation methods and by using adaptive optics system on basis piezooptic segmented mirror. The optic wavefront correction was sufficient to create higher order aberrations as spherical and coma.There was moderate correlation between diameter ratio of two blood vessels assessed by two ophthalmologists.

We conclude that ophthalmologist when examining fundus of an eye must pay attention to both patient’s aberrations and also those of examiner.

* In cooperation with Department of Optometry and Vision Science, University of Latvia.

** Laboratory of Adaptive Optics, Moscow State University, Moscow, Russia.

–  –  –

In early 1907 - Nagel offered new way to diagnose red - green colour vision defects, offering a device called anomaloscope. Using this equipment in practice it is possible to distinguish protanopia from deuteranopia also protanomaly from deuteranomaly with best available accuracy.



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