Showing papers in "Ferroelectrics in 2005"
TL;DR: In this article, the properties of perovskite ferroelectrics Na0.5Bi 0.5TiO3 (NBT), K0.4B4 + O3 (KBT) and their solid solutions are reviewed.
Abstract: Properties of the perovskite ferroelectrics Na0.5Bi0.5TiO3 (NBT), K0.5Bi0.5TiO3 (KBT) and their solid solutions are reviewed. Consideration of the NBT behavior draws attention to phenomena of the ion ordering, coexistence of several phase regions within a crystal lattice, phase transition diffusion and to a quite new phenomenon: existence of the isotropization points (temperatures) in the AFE-phase-temperature interval. In the KBT the isotropic points are absent. NBT, KBT, and their solid solutions are considered as possible useful materials for technical (in particular, for piezoelectric) applications. There are also some other A0.5 +Bi0.5B4+O3 perovskites which are interesting for future research.
203 citations
TL;DR: In this article, the frequency dependent properties of large numbers of resistor-capacitor (R-C) networks were investigated, with particular emphasis on observed power-law behavior and a comparison with previous work.
Abstract: It has been shown that the universal dielectric response (UDR) of heterogeneous materials can be reproduced by electrical networks consisting of randomly positioned resistor and capacitors. The random network represents a microstructure that contains both insulating (the capacitor) and conductive regions (the resistor). This paper presents an investigation into the frequency dependent properties of large numbers of resistor-capacitor (R-C) networks. Parameters investigated include permittivity, conductivity and phase angle, with particular emphasis on observed power-law behavior and a comparison with previous work in this area.
78 citations
TL;DR: In this paper, theoretical considerations of structural order in sintered hydroxyapatite (HA) were reported and it was shown that in addition to the non polar P21/b phase HA can also exist as a polar phase.
Abstract: Disorder of the OH− ion orientation is inherent in the currently accepted structure of hydroxyapatite (HA), hexagonal P63/m. In the case of local ordering in the OH− ion orientation, the resulting structure will be a monoclinic P21/b, with an alternate orientation of OH− columns in the b-direction. Both of these proposed structures are electrically non polar and fail to explain the polarisation phenomena observed in HA. Here we report some theoretical considerations of structural order in HA and show that in addition to the non polar P21/b phase HA can also exist as a polar phase. Various physical properties including static dielectric constant and polarisation are simulated from empirical interatomic potential calculations and used to explain the observed dielectric anomaly in sintered hydroxyapatite.
70 citations
TL;DR: In this article, a bibliography is given containing 2067 references published during 2002 and 2003 on piezoelectric and pyroelectric properties of materials and their applications, which contains listings of journal articles with complete bibliographic citations.
Abstract: A bibliography is given containing 2067 references published during 2002 and 2003 on piezoelectric and pyroelectric properties of materials and their applications. It contains listings of journal articles with complete bibliographic citations. This bibliography is the continuation of a series published semi-annually.
47 citations
TL;DR: Ferroelectric and ferroelastic phase transitions in molybdates and tungstates of monovalent and bivalent elements are reviewed in this paper, where the nature and peculiarities of these transitions are briefly discussed.
Abstract: Ferroelectric and ferroelastic phase transitions in molybdates and tungstates of monovalent and bivalent elements are reviewed. The nature and peculiarities of these transitions are briefly discussed. Most of interesting phase transitions are observed in compounds, containing monovalent ions, while among compounds of bivalent elements, only perovakites have properties of interest. Some molybdates and tungstates under consideration are improper ferroelectrics and ferroelastics, some of them have non-reversible, but reorienting, spontaneous polarization, some have modulated phases. There are indications on possibility of the ferroelectric state formation as a result of a reconstructive phase transition. Some crystal chemical problems are briefly discussed.
46 citations
TL;DR: In this article, phase transitions in binary molybdates and tungstates of mono-and trivalent elements are reviewed with a special attention to ferroelastic and ferroelectric behavior.
Abstract: Phase transitions in binary molybdates and tungstates of mono- and trivalent elements, as well as some of their physical properties are reviewed with a special attention to ferroelastic and ferroelectric behavior. There are many compounds with phase transitions of the displacement type and reconstructive ones. The author tried to pick out only compounds with the displacement-type transitions. This allowed the identification of many compounds interesting for physics of ferroelasticity and ferroelectricity among the structure families of scheelite, glaserite, palmierite, wolframite etc. So far, they have been studied in the main (better or worse) by chemists. Now physisists have to study them.
45 citations
TL;DR: Barium titanate ceramics were prepared through mechanochemical synthesis starting from fresh prepared barium oxide and titanium oxide in rutile form as discussed by the authors, and a mixture of oxides was milled in zirconia oxide jar in the planetary ball-mill during 30, 60, 120 and 240 min. Extended time of milling directed to formation of higher amount of barium titanates perovskite phase.
Abstract: Barium titanate ceramics were prepared through mechanochemical synthesis starting from fresh prepared barium oxide and titanium oxide in rutile form. Mixture of oxides was milled in zirconia oxide jar in the planetary ball-mill during 30, 60, 120 and 240 min. Extended time of milling directed to formation of higher amount of barium titanate perovskite phase. Barium titanate with good crystallinity was formed after 240 min. Sintering without pre-calcinations step was performed at 1330°C for 2 hours with heating rate of 10°C/min. The XRD, DSC, IR and TEM analyses were performed. Electric and ferroelectric properties were studied. Very well defined hysteresis loop was obtained.
35 citations
TL;DR: In this article, the authors fabricated poly-L-lactic acid (PLLA) fiber samples using high-speed spinning in order to improve their piezoelectricity.
Abstract: We fabricated poly-L-lactic acid (PLLA) fiber samples using high-speed spinning in order to improve their piezoelectricity. If an electric field is applied to the PLLA fiber in the direction perpen...
35 citations
TL;DR: In this paper, a lead-free piezoceramic material based on potassium sodium niobate (K,Na)NbO 3 has been developed, which has a low theoretical density, leading to a relatively low acoustic impedance.
Abstract: The market for piezoceramic components is dominated by lead zirconate titanate (PZT) materials containing more than 60 wt% lead. Since lead is a toxic heavy metal, it has become a great concern how to eliminate the use of PZT by replacing it by non-harmful materials while maintaining comparable piezoelectric properties. This was the objective of the European LEAF project within the GROWTH programme, ending in February 2004. In this project, alkali niobates were proposed as alternative piezoceramic materials, and special emphasis was given to potassium sodium niobate, (K,Na)NbO 3 . Among the interesting properties of this system is a low theoretical density, leading to a relatively low acoustic impedance of 24 MRa. The partners of the project have developed lead-free ceramics based on potassium sodium niobate that can be a competitive alternative to PZT for certain applications. A selection of obtained properties, examples of industrial applications and an overview of end-user considerations will be presen...
33 citations
TL;DR: In this paper, a description of present efforts to make thin-films for ferroelectric memory devices into truly three-dimensional objects, such as nano-tubes, nano-rods, and nano-ribbons, is presented.
Abstract: A description is presented of present efforts to make thin-films for ferroelectric memory devices into truly three-dimensional objects, such as nano-tubes, nano-rods, and nano-ribbons. These may have important applications for DRAM trenched capacitors. A summary of state-of-the-art magnetic RAM (MRAM) and ferroelectric FRAM devices is included.
29 citations
TL;DR: In this article, a band structure of barium titanate was calculated with the WIEN2k program, using FP LAPW method, and it was found that the transition between cubic and tetragonal structures does not change significantly either the bands widths or their positions in relation to the Fermi level.
Abstract: A band structure of barium titanate crystal has been calculated with the WIEN2k program, using FP LAPW method. A broad dispersion of the valence band (about 5 eV) and a narrow forbidden energy gap (about 2 eV) confirm the crucial role of covalent interactions in this compound. The calculations have been performed for cubic and tetragonal structures of the crystal, which have allowed to determine the changes in the electronic structure due to the ferroelectric phase transition. It is found that the transition between cubic and tetragonal structures does not change significantly either the bands widths or their positions in relation to the Fermi level. The main difference concerns the character of the bands and is clearly related to the oxygen electronic states. This indicates that the ferroelectric behavior of the material may be explained by the crucial role of the π bonds formed by the oxygen ions. The band structure obtained remains in direct relation to the molecular picture thus confirming ligand fiel...
TL;DR: In this paper, X-ray diffraction analysis of polycrystalline samples of Pb 3 R 3 Ti 5 Nb 5 O 30 (R = La and Sm) have been synthesized by a high-temperature solid-state reaction technique.
Abstract: Polycrystalline samples of Pb 3 R 3 Ti 5 Nb 5 O 30 (R = La and Sm) have been synthesized by a high-temperature solid-state reaction technique. X-ray diffraction (XRD) analysis of the compounds showed the formation of single phase compounds in an orthorhombic crystal structure. Studies of dielectric constant (ϵ) of the above compounds as a function of temperature (25 to 375°C) at 10 kHz exhibit a ferroelectric phase transition of diffuse type. Temperature variation of dc resistivity/conductivity shows that these compounds exhibit negative temperature coefficient of resistance (NTCR).
TL;DR: The effect of strontium doping in K 05 Na 05 NbO 3 (KNN) ceramics in the amount of 05, 2, 5 and 10 atom % is studied in this paper.
Abstract: The effect of strontium doping in K 05 Na 05 NbO 3 (KNN) ceramics in the amount of 05, 2, 5 and 10 atom % is studied With increasing dopant content the orthorhombic distortion of the perovskite solid solution is markedly reduced The density of stoichiometric KNN sintered at 1115°C is 944% of TD, doping with 05% Sr leads to a 2% higher density, but with higher amounts of Sr the density decreases The values of ϵ and d 33 for the undoped KNN ceramics are 450 and 80 pC/N, respectively Sr—doping causes an increase in the dielectric constant, from 500 for KNN-05% Sr to 1650 for KNN-5% Sr and a decrease in the d 33 constant from 95 to 50 pC/N
TL;DR: SrBi 2 Nb 2 O 9 and KTa 1− x Nb x O 3 thin films were grown by pulsed laser deposition on various substrates in this article, which showed a strong effect of the structural characteristics on the dielectric behavior.
Abstract: SrBi 2 Nb 2 O 9 and KTa 1− x Nb x O 3 thin films were grown by pulsed laser deposition on various substrates. Structural investigations evidenced that single phase polycrystalline randomly oriented films were grown on sintered alumina whereas epitaxial films were grown on (100)MgO. The microstructure was strongly controlled by the structural characteristics. Interdigited capacitors patterned on SrBi 2 Nb 2 O 9 films on both substrates as well as permittivity and losses measurements performed at 12.5 GHz showed a strong effect of the structural characteristics on the dielectric behavior.
TL;DR: In this article, a discussion of nano-scale ferroelectric devices is presented, where it is shown that nano-ribbons exhibit an extra relaxation process with an 0.20 ± 0.01 eV activation energy attributed to OH hydroxyl ion reorientation.
Abstract: A discussion is presented of nano-scale ferroelectric devices. Nano-ribbons exhibit an “extra” relaxation process with an 0.20 ± 0.01 eV activation energy attributed to OH hydroxyl ion reorientation. Barium titanate single crystals down to 65-nm are characterized by bulk properties, and broadening of dielectric peaks ϵ(T) versus temperature attributed by others to intrinsic depolarization effects are instead shown to be extrinsic, due to oxygen vacancy gradients, in accord with the recent models of Catalan et al. and of Bratkovsky and Levanyuk. Similar transitions in barium strontium titanate (BST) thin films are shown to be reentrant (only upon warming from T < 50 K) and limited by kinetics, not thermodynamic equilibria.
TL;DR: In this article, the influence of thermal annealing on pyroelectric properties of PVDF and P(VDF-TrFE) 75-25 copolymer polymers was studied.
Abstract: The aim of this work is to study the influence of thermal annealing on pyroelectric properties of PVDF and P(VDF-TrFE) 75–25 copolymer. A strong dependence of pyroelectricity decay upon ageing temperature and time is observed. There is no decay for ageing temperatures lower than +50°C for both polymers. A slower decay of P(VDF-TrFE) 75–25 copolymer pyroelectric properties are is observed for ageing temeperatures T a ≤ +110°C, i.e. lower than the Curie transition point (+128°C). The strong decay of the pyroelectric coefficient observed in PVDF is mainly due to shrinkage effects occuring at the α c -transition. The TSC study performed highlighted that changes of crystallinity occur only for high ageing temperatures (> 110°C).
TL;DR: Based on the dielectric and X-ray diffraction data, phase diagram of the BaTiO3-La(Mg1/2Ti 1/2)O3 series has been determined.
Abstract: Ceramics of (1 − x)BaTiO3−xLa(Mg1/2Ti1/2)O3 series (x = 0, 0.025, 0.05, 0.075 and 0.1) were dielectrically investigated. Based on the dielectric and X-ray diffraction data, phase diagram of the system for the studied composition range has been determined. Apparent relaxor behavior was revealed to set in when the BaTiO3-type sequence of three phase transitions is reduced to only diffuse transition. No clear boundary was found between ferroelectric and relaxor compositions of the system. It was observed the continuous crossover from ferroelectric to relaxor behavior.
TL;DR: In this article, the switching in one monolayer of ferroelectric vinylidene fluoride-trifluoroethylene copolymer P[VDF-TrFE] is observed.
Abstract: The switching in one monolayer of ferroelectric vinylidene fluoride-trifluoroethylene copolymer P[VDF-TrFE] is observed. The kinetics of switching is well described by Landau-Khalatnikov (LK) equation.
TL;DR: In this paper, dielectric ceramics with compositions belonging to the Ba(Nd x Ti1−2x Nb x )O 3 with varying concentration of x were prepared through Solid State Sintering route using both conventional and microwave sintering.
Abstract: Dielectric ceramics with compositions belonging to the Ba(Nd x Ti1−2x Nb x )O 3 with varying concentration of x were prepared through Solid State Sintering route using both conventional and microwave sintering. The phase transformations were studied by dielectric measurements in a wide range of temperature and frequency. The relaxor behaviour is almost favoured as the composition deviates more from BaTiO 3 and as the substitution is heterovalent in the 6-coordination number crystallographic site.
TL;DR: In this paper, the authors used finite element simulation and Monte Carlo methods to calculate the effective permittivity (ϵ) and tangent loss (tan(δ)) of a composite dielectric.
Abstract: Finite Element Simulation and Monte-Carlo methods are used to calculate the effective permittivity (ϵ) and tangent loss (tan(δ)) of a composite dielectric. Wakino et al. has used this approach to study the dependence of ϵ on volume ratio and compared it with the Series, Parallel and Lichteneker formula. In this paper, the modeling has been further extended to include tan(δ) also, and the results are compared to well known Effective Medium and Empirical Models. For ϵ, it was found that both the symmetric Bruggeman and Wakino formula are close to the numerical results for all volume fractions (f). For tan (δ), the numerical results follow the typical pattern of symmetric Bruggeman formula. There is also found to be a logarithmic relationship between the effective permittivity and tangent losses.
TL;DR: In this article, it has been observed that the loss factor of CCTO can be reduced by B 2 O 3 addition and also the temperature dependence of dielectric constant is minimized by boron addition.
Abstract: The recently discovered giant dielectric CaCu 3 Ti 4 O 12 (CCTO) has been reported to show dielectric constant value as high as 80,000 for single crystals and around 10,000 for ceramics. However the dielectric constant is also associated with high dissipation factor. In the present study, it has been observed that the loss factor of CCTO can be reduced by B 2 O 3 addition. The low frequency dispersion of CCTO ceramics, which indicates Maxwell-Wagner type relaxation, is reduced by boron addition. Also the temperature dependence of dielectric constant is minimized by boron addition. From the present work it can be surmised that B 2 O 3 addition can favourably modify the dielectric properties of CCTO ceramic for its practical applications as a capacitor material.
TL;DR: In this paper, the authors studied the switching under application of bipolar ac field by recording the hysteresis loops in wide temperature and field range in PLZT x/65/35 ceramics.
Abstract: The switching under application of bipolar ac field is studied by recording of the hysteresis loops in wide temperature and field range in PLZT x/65/35 ceramics. The qualitative difference of the shape of hysteresis loops above and below the freezing temperature is attributed to backswitching in relaxor phase due to the depolarization field produced by the bound charges located at the interphase boundaries. The application of the quasistatic approach to analysis of the experimental data allows us to obtain parameters of the distribution function of local coercive fields from the field dependence of the switching charge derivative on field.
TL;DR: In this article, a correlation between the densification rate and microstructure evolution of mechanically activated BaTiO 3 has been analyzed using a dilatometer and a scanning electron microscope (SEM).
Abstract: Increasing demands on the quality of electronic ceramics requires a well-controlled correlation between particle morphology and processing conditions. Since mechanical activation is one of the methods for modification of physico-chemical properties of dispersed systems, in this study a correlation between the densification rate and microstructure evolution of mechanically activated BaTiO 3 has been analyzed. The shrinkage behaviour of mechanically activated samples, sintered under non-isothermal conditions has been analyzed by a sensitive dilatometer. Densification rate as a function of relative density for different activation times has been calculated. Microstructure investigations of sintered samples were carried out, using a scanning electron microscope (SEM). The presented results enable establishing processing parameters that are indispensable for obtaining materials with advanced properties.
TL;DR: In this paper, an analysis of the factors governing variation in T c and P s of PbTiOO3, KNbO3 and BaTiO3 members of ABO3 perovskite family considering the parameters like tolerance factor, t, electronic configuration, electronegativity, polarizability and character of bonding using molecular orbital theory was performed.
Abstract: Qualitative analysis of the factors governing variation in T c and P s of PbTiO3, KNbO3 and BaTiO3 members of ABO3 perovskite family considering the parameters like tolerance factor, t, electronic configuration, electronegativity, polarizability and character of bonding using molecular orbital theory (MOT) reveals that (i) T c and P s vary inversely with t, (ii) increased interaction between ions decreases t as packing in unit cell increases, (iii) the size of A and B cations and their interaction with oxygen governs the ferroelectric behaviour, (iv) the covalent interaction between A─O and B─O is responsible for the other transitions in the ferroelectric phase and (v) the occurrence of P s is due to the presence of mixed ionic-covalent B─O bonds.
TL;DR: In this article, PZT-PVDF composites of 0-3 connectivity are fabricated using PZTs synthesized in a laboratory and commercially available PZTS powders (3 types).
Abstract: PZT-PVDF composites of 0-3 connectivity are fabricated using i) PZT powder synthesized in our laboratory and ii) commercially available PZT powders (3 types). Hot-Press technique is used for the preparation of 0-3 composites. The PZT powder is synthesized by ‘Wet grinding Solid State Thermal Reaction’ method. The piezoelectric coefficients and dielectric constant of the composites prepared using the PZT powder synthesized in the laboratory are compared with those prepared using commercial PZT powders. The study is focused on two aspects: Effect of the phase of PVDF (α,β and γ) on the properties of the composites Effect of poling filed on the properties of the composites The piezoelectric coefficients and dielectric constant are studied as a function of volume fraction of PZT.
TL;DR: In this paper, the dielectric spectrum of mixed CuInP2(S0.7Se0.3)6 crystals was investigated and the calculated distribution of relaxation times confirmed glassy behaviour and the maxima of the distribution of the relaxation times follow Vogel-Fulcher law with parameters: activation energy E A = 9.4 · 10−2 eV, dipole freezing temperature T 0 = 21.9 K and attempt frequency υ0 = 1/(2π τ0) = 0.149 THz.
Abstract: The dielectric spectrum of mixed CuInP2(S0.7Se0.3)6 crystals was investigated. The calculated distribution of relaxation times confirms glassy behaviour and the maxima of the distribution of the relaxation times follow Vogel-Fulcher law with parameters: activation energy E A = 9.4 · 10−2 eV, dipole freezing temperature T 0 = 21.9 K and attempt frequency υ0 = 1/(2π τ0) = 0.149 THz. From all presented results we see, that CuInP2(S0.7Se0.3)6 crystal shows typical dipolar glass dielectric dispersion and we may conclude that this crystal belongs to new family of materials that exhibits a dipolar glass behavior.
TL;DR: In this article, the electrical properties of conducting polyaniline/BaTiO 3 composites are characterized using various techniques such as SEM, XRD and IR spectroscopy.
Abstract: Conducting polyaniline/BaTiO 3 (PANI/BT) composites have been synthesized by ‘in situ’ deposition technique by placing fine graded BaTiO 3 in polymerization mixture of aniline. The composites are characterized using various techniques such as SEM, XRD and IR spectroscopy. The electrical properties such dc conductivity and ac conductivity are studied by sandwitching the pellets of these composites between the silver electrodes. It is observed that in both the cases the values of conductivities increases up to 30 weight % of BaTiO 3 in polyaniline and decreases thereafter. Initial increment in conductivity is due to extended chain length of polyaniline where polarons possess sufficient energy to hop between favorable sites. Beyond 30 weight % of BaTiO 3 in polyaniline, the blocking of charge carriers takes place reducing the conductivity values. The polyaniline/ BaTiO 3 composites are poled by applying constant voltage for a fixed time to study their electrical hysteresis characteristics. It is observed tha...
TL;DR: In this paper, a non-classic exponent a = δ/(δ −1) = 1.62 for strontium titanate in the vicinity of Tc≈25 K.
Abstract: Some novel features of strontium titanate are presented. First, it reveals secondary ferroicity when exposed to an external electric field in its tetragonal paraelectric state. It is shown on isotopically doped SrTi 18 O 3 (STO18) that odd-oriented ferroelastic domains can be switched under anomalously large electrostriction such as to create a perfect axially orientated state. Second, the strong non-linear dielectric response of STO18 can be described within the frame of a classic equation of state involving a nonlinearity coefficient with non-classic temperature dependence after correction for a contribution to random-field induced polar nanoregions. Third, static nonzero-external field scaling analysis reveals a non-classic exponent a = δ/(δ −1) = 1.62 when respecting the validity of the quantum temperature concept in the vicinity of Tc≈25 K. Fourth, polarized microscopy confirms that the isotope-induced ferroelectric low temperature phase is probably triclinic rather than orthorhombic. This results fr...
TL;DR: In this paper, the dielectric response of (0-3) type composites, made of BaTiO 3 particles with mean size of 20-30 nm and polyvinylidene fluoride was determined by the response with a broad Cur...
Abstract: Dielectric response of (0–3) type composites, made of BaTiO 3 particles with mean size of 20–30 nm and polyvinylidene fluoride was found to be determined by the response of BaTiO 3 with a broad Cur...
TL;DR: In this article, a review of the research on the barium-strontium niobate films and multilayer structures performed in the institutes of the Siberian Branch of Russian Academy of Sciences is presented.
Abstract: A brief review of the research on the barium-strontium niobate films and multilayer structures performed in the institutes of the Siberian Branch of Russian Academy of Sciences is presented. The electrophysical properties of the films are studied, as well as characteristics of the microelectronic components such as memory elements, pyroelectric radiation receivers, electrooptic light modulators and electrostatic micromotors that are based on these films.