Stochastic model of dispersive multi-step polarization switching in ferroelectrics due to spatial electric field distribution

A stochastic model for polarization switching in tetragonal ferroelectric ceramics is introduced, which includes sequential 90{\deg}- and parallel 180{\deg}-switching processes and accounts for the dispersion of characteristic switching times due to a nonuniform spatial distribution of the applied field. It presents merging of the recent multistep stochastic mechanism (MSM) with the earlier nucleation limited switching (NLS) and inhomogeneous field mechanism (IFM) models. The new model provides a much better description of simultaneous polarization and strain responses over a wide time window and a deeper insight into the microscopic switching mechanisms, as is exemplarily shown by comparison with measurements on lead zirconate titanate.Comment: 11 pages, 3 figure

Influence of meristem culture and virus elimination on phenotypical modifications of grapevine (Vitis vinifera L., cv.Refošk)

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Characterisation of cv. Refosˇk (Vitis vinifera L.) by SSR markers

Fifty-five accessions of cv. Refošk from a clonal selection vineyard in the Karst district (Slovenia) were screened by 6 SSR markers in order to assess their uniformity. Two of the accessions showed different patterns (Clone 7 and Clone 50), while 53 accessions revealed identical SSR allelic profiles. Four of the uniform and the two different accessions were compared to 11 Refošk types from adjacent regions (Slovenia (Koper), Croatia and Italy) using 23 SSR markers. The SSR analysis revealed 7 identical genotypes (4 uniform Karst clones, one Italian and two Koper types), while three Koper (Slovenia) and three Italian types, as well as Teran from Croatia, showed genetic polymorphisms on an intra-varietal level. Clone 7, Clone 50 and Sladki Teran (Croatia) showed highly diverse genetic patterns from other types and should be considered different varieties. Comparative analysis allowed reliable construction of the predominant Refošk type grown in Slovenia.

Fish pass designing according to latest guidelines

Many fish species undertake migrations as part of their basic behavior. In addition to the long migratory routes, many species of fish and other aquatic organisms migrate in the medium and short distances, especially from one part of the watercourse to the other. Migration can take place due to various reasons and factors in certain phases of life cycle of aquatic organisms. People have started to interrupt the longitudinal connectivity of watercourses by building barriers and dams for their own needs and so destroyed many centuries of migratory habits of aquatic organisms. The aim of the construction of fish passes is to mitigate the consequences of the building dams and barriers to achieve free passes for all aquatic organisms in rivers and streams. However It should be noted that every construction of a properly functioning fish passes is always just a second-best solution and does not replace natural connectivity. Fish passes are therefore structures that facilitate upstream and downstream migration of aquatic organisms over obstacles and barriers. Fish passes can be designed as technical fish passes, which are more artificial types or close-to-nature types. Both types of fish passes try to create the best possible imitation of natural conditions that are specific for watercourse in a particular area

Microsatellite genotyping of old Slovenian grapevine varieties (Vitis vinifera L.) of the Primorje (coastal) winegrowing region

Thirty-three grapevine varieties from Slovenia were genotyped at 21 microsatellite loci in order accurately to identify varieties and to evaluate their synonyms and homonyms, including varieties cultivated in neighbouring countries. Among Slovenian varieties some previously assumed synonyms were confirmed and some new ones were discovered: ‘Poljšakica Drnovk’ = ‘Istrska Malvazija’, ‘Pikolit Italy’ = ‘Pikolit Vienna’, ‘Vitovska grganja’ = ‘Racuk’ and ‘Prosecco’ = ‘Glera’ = ‘Števerjana’. Types of Zelen (‘Zelen Pokov’, ‘Zelen 66’ and ‘Zelen 2.4’) were distinct at several microsatellite loci so can only be considered to be homonyms. Two ‘Picolit’ types were considered to be ‘true-to-type’ on the basis of comparison with ‘Picolit’ clones from Italy. Synonymy between ‘Heunisch’ and ‘Belina’ was not confirmed in our study, since ‘Belina Pleterje’ differentiated from ‘Heunisch weiss’ at 13 out of 19 loci. Comparison of ‘Vitovska grganja’ from Slovenia with ‘Vitouska’ from Italy also showed dissimilarities at the majority of the analysed loci.

Electromechanical properties of Ce-doped (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 lead-free piezoceramics

Abstract Lead-free piezoceramics based on the (Ba, Ca)(Zr, Ti)O3 (BCZT) system exhibit excellent electromechanical properties for low-temperature actuation applications, but suffer from relatively high processing temperatures. Here we demonstrate an approach for the reduction of the sintering temperature and simultaneous increase of the electromechanical strain response of (Ba, Ca)(Zr, Ti)O3 piezoceramics by aliovalent doping with Ce. The samples were prepared by solid state synthesis and their crystallographic structure, dielectric, ferroelectric, and electromechanical properties were investigated. The highest d*33 value of 1189 pm/V was obtained for the sample with 0.05 mol% Ce, substituted on the A-site of the perovskite lattice. The results indicate a large potential of these materials for off-resonance piezoelectric actuators

Stochastic multistep polarization switching in ferroelectrics

Consecutive stochastic 90° polarization switching events, clearly resolved in recent experiments, are described by a nucleation and growth multistep model. It extends the classical Kolmogorov-Avrami-Ishibashi approach and includes possible consecutive 90°- and parallel 180° switching events. The model predicts the results of simultaneous time-resolved macroscopic measurements of polarization and strain, performed on a tetragonal Pb(Zr,Ti)O3 ceramic in a wide range of electric fields over a time domain of seven orders of magnitude. It allows the determination of the fractions of individual switching processes, their characteristic switching times, activation fields, and respective Avrami indices

Orienting anisometric pores in ferroelectrics:Piezoelectric property engineering through local electric field distributions

Ferroelectrics are a technologically important class of materials that are used in actuators, sensors, transducers, and memory devices. Introducing porosity into these materials offers a method of tuning functional properties for certain applications, such as piezo- and pyroelectric sensors and energy harvesters. However, the effect of porosity on the polarization switching behavior of ferroelectrics, which is the fundamental physical process determining their functional properties, remains poorly understood. In part, this is due to the complex effects of porous structure on the local electric field distributions within these materials. To this end, freeze-cast porous lead zirconate titanate (PZT) ceramics were fabricated with highly oriented, anisometric pores and an overall porosity of 34 vol.%. Samples were sectioned at different angles relative to the freezing direction, and the effect of pore angle on the switching behavior was tracked by measuring simultaneously the temporal polarization and strain responses of the materials to high-voltage pulses. Finite-element modeling was used to assess the effect of the pore structure on the local electric field distributions within the material, providing insight into the experimental observations. It is shown that increasing the pore angle relative to the applied electric field direction decreases the local electric field, resulting in a reduced domain-wall dynamic and a broadening of the distribution of switching times. Excellent longitudinal piezoelectric (d33 = 630 pm/V) and strain responses (Sbip = 0.25% and Sneg = 0.13%, respectively), comparable to the dense material (d33 = 648 pm/V, Sbip = 0.31%, and Sneg = 0.16%), were found in the PZT with anisometric pores aligned with the poling axis. Orienting the pores perpendicular to the poling axis resulted in the largest reductions in the effective permittivity (εσ33= 200 compared to εσ33= 4100 for the dense PZT at 1 kHz), yielding the highest piezoelectric voltage coefficient (g33 = 216×10−3 Vm/N) and energy-harvesting figure of merit (d33g33 = 73×10−12 m2/N). These results demonstrate that a wide range of application-specific properties can be achieved by careful control of the porous microstructure. This work provides an understanding of the interplay between the local electric field distribution and polarization reversal in porous ferroelectrics, which is an important step towards further improving the properties of this promising class of materials for sensing, energy harvesting, and low-force actuators