Antiferroelectric Crystal Research Articles

Dielectric, Elastic and Electromechanical Properties of K1-x(NH4)xH2PO4 Solid Solutions in Paraelectric Phase

Temperature dependences of dielectric permittivity ϵ33, piezoelectric constant d36 and elastic compliance S66 of K1-x(NH4)xH2PO4 ferro – antiferroelectric (FE - AFE) mixed crystals have been studied within temperature range 30 – 300 К. It was found a considerable contribution of the strain component x6 to polarization P3 near the FE transition temperature due to piezoelectric effect. Piezoelectric contribution to dielectric response in the vicinity AFE phase transition is weaker. It leads, in particular, to difference in the both shapes and positions of ϵ33 and S66 anomalies for K0,25(NH4)0,75H2PO4 single crystal near the transition temperature.

Effect of resistive switching and electrically driven insulator–conductor transition in PbZrO3 single crystals

AbstractIn this work, the results of detailed investigations of classical current–voltage characteristics measured both on the macro‐ and nanoscale with the use of LC‐AFM microscopy are presented. With decreasing frequencies abnormal hysteresis I(V) loops in a PbZrO3 single crystal were observed, showing a bipolar resistive switching behavior. The observed phenomena have been accounted for by the nonstoichiometry and defects produced electrochemically in the surface layers. Due to the nonstoichiometric composition of the crystal surface we showed the possibility of reversible transformation from an insulating to a conducting state in an antiferroelectric crystal by an electroforming process. The model of filamentary structure produced by extended defects and an electrochemical process is applied here to explain the data.

Brillouin spectroscopic study of central peak in NaNbO3 single crystal

Anti-ferroelectric NaNbO3 single crystals were grown by flux method. Brillouin spectroscopy was used for the first time to investigate the central peak in both P and R phases and across P–R phase transition temperature TC at 643K. The temperature dependence of relaxation time and that of integrated intensities of central peak (CP) are found to show anomalies across TC. The relaxation time of CP shows a critical slowing down in the vicinity of phase transition implying the nature of the transition to be order–disorder type. An activation energy for the Nb-ion movement between two equivalent sites is estimated to be 105±10meV. In addition, a comparison of the temperature evolution of integrated intensities of CP and low frequency modes suggest that these are uncoupled.

Induced growth of Pb0.97La0.02(Zr0.66Sn0.27Ti0.07)O3 antiferroelectric single crystals with a platinum wire

Relaxor antiferroelectric (Pb,La)(Zr,Sn,Ti)O3 (PLZST) with the composition near the morphotropic phase boundary shows excellent electrical properties. However, the crystal growth of PLZST is limited by the incongruent melting of the materials. Crystal growth of PLZST was induced by a platinum wire in the flux solution with 50 wt% PbO-PbF2-B2O3 as a solvent. The obtained PLZST single crystals are optical transparent with light yellow color. The size of the crystals in regular rectangular shape varies from 0.5 mm to 1 mm. The PLZST single crystals exhibit tetragonal phase structure. The element contents of the crystals were measured by inductively coupled plasma atomic emission spectrometry. The results show that the composition of as-grown crystals is a little bit deviated from the starting composition. The single crystals show two dielectric peaks at 115 °C and 182 °C, corresponding to antiferroelectric-ferroelectric and ferroelectric-paraelectric phase transitions. The dielectric data of as-grown crystals indicate there is typical relaxor behavior near 182 °C. The value of relaxor factor n is 1.49642.

Growth and characterization of Pb0.97La0.02(Zr0.66Sn0.27Ti0.07)O3 antiferroelectric single crystals

Single crystals of Pb0.97La0.02(Zr0.66Sn0.27Ti0.07)O3 (PLZST) with the composition near the morphotropic phase boundary were grown by the flux method. The PbO–PbF2–B2O3 system was used as a solvent. PLZST single crystals with the size of 4–6 mm are obtained and these crystals are slightly translucent after polishing. The splitting of (200) reflection peak indicates that the obtained crystals are of a single phase with tetragonal perovskite structure. The element contents of the grown crystals were measured by inductively coupled plasma atomic emission spectrometry. The chemical composition of the crystals is Pb0.979La0.014(Zr0.666Sn0.285Ti0.049)O3. Thermal properties and dielectric properties of PLZST single crystals were studied. The results show that flux-grown PLZST single crystals exhibit obvious endothermic processes and relaxor behaviors near the phase transition temperatures.

Progress in lead-based ferroelectric and antiferroelectric single crystals: composition modification, crystal growth and properties

Ferroelectric and antiferroelectric materials, with complex perovskite structures, have experienced wide interest due to their peculiar structure and properties. In this highlight, recent advances of these two types of materials are reviewed, with particular emphasis on piezoelectrics/ferroelectric and antiferroelectric single crystals, owing to their ultra-high electric properties for practical application. Relaxor ferroelectric single crystals, represented by Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) at compositions near the morphotropic phase boundary (MPB), possess a high piezoelectric constant d33 (>2000 pC N−1) and electromechanical coupling factors k33 (90–92%). However, a low ferroelectric phase transition temperature Tr-t, far below the Curie temperature Tc restricts its further application in a broad temperature range. Some work on the design of a new pseudo-ternary system of Pb(Mg1/3Nb2/3)O3–PbZrO3–PbTiO3 (PMN-PZ-PT) and Pb(Mg1/3Nb2/3)O3–Pb(Fe1/2Nb1/2)O3–PbTiO3 (PMN-PFN-PT) have been demonstrated with emphasis on the composition modification and crystal growth. Moreover, for relaxor antiferroelectrics represented by (Pb,La)(Zr,Sn,Ti)O3 (PLZST) it is very difficult to grow bulk and high quality single crystals because of its incongruent melting. Our recent investigations on the flux growth of PLZST single crystals, especially the flux selection, compositions optimization, and defect analysis of as-grown single crystals are also described in this highlight.

Features of the behavior of longitudinal static and dynamic dielectric, piezoelectric, and elastic characteristics of KH2PO4 and NH4H2PO4 crystals

Along with their electromechanical coupling coefficients, the longitudinal dielectric, piezoelectric and elastic characteristics in ferroelectric KH2PO4 and antiferroelectric NH4H2PO4 crystals are calculated using a modified proton ordering model that considers piezoelectric coupling and the four-particle cluster approximation. The possibility of detecting piezoactivity in solid solutions of K1 − x(NH4)xH2PO4 is substantiated.

Density functional study of weak ferromagnetism in a thick BiCrO3 film

Very thick films of BiCrO3 have been grown on a SrTiO3 substrate, maintaining a tetragonal lattice up to thicknesses of 14,000 Å. Assuming that we can treat films of this thickness as bulk crystals, we first calculated the experimentally undetermined atomic positions within the unit cell with the measured lattice constant of the film, and then relaxed the lattice constants along with the atomic positions. All of the calculations result in an antiferroelectric crystal with the Pnma space group with noncollinear Bi displacements. We find G-type antiferromagnetism with a spin-orbit induced weak ferromagnetic component; however, the weak ferromagnetic component can be canceled if the antiferromagnetic spins are oriented along a particular one of the three twofold rotation axes.

Strong nonlinear electrostriction in PbZr1− x Sn x O3 antiferroelectric crystals with 0.11 < x < 0.35

For antiferroelectric crystals of PbZr1− x Sn x O3 with 0.11 < x < 0.35 the measurements of electrostrictive strain e 11 have been performed in the paraelectric phase. The experiments showed a departure of the temperature dependence of the electrostrictive field-related coefficient M 11(T ) from that expected by theory. A strong nonlinear increase in the polarization-related electrostrictive coefficient Q 11 when approaching Tε max has been found. This unusual behavior was related to the pre-transitional effects connected to the presence of polar micro/nanoregions. Nature and dynamics of these regions are directly related to the Sn concentration in the crystals.

Growth and characterization of (Pb, La)(Zr, Sn, Ti)O3 single crystals

Relaxor antiferroelectric single crystals, lead lanthanum zirconate stannate titanate (PLZST), with compositions near the morphotropic phase boundary (MPB) were grown by the flux method using PbO–PbF2–B2O3 as a flux. Pale yellow single crystals, which were pseudo-cubes of 1.5–2mm length and 1–2mm thickness, were obtained. Their morphologies and chemical compositions were studied. Compositional deviation was found to occur during crystal growth. The fitted curve of the Ti4+ content in crystals versus that of in raw materials suggested that the chemical composition could draw near to MPB by adding a large amount of Ti4+ in the raw materials. XRD patterns revealed that the calcined powders experienced a gradual phase transition process from tetragonal to rhombohedral with increase in Ti4+ content. Tetragonal phase structures existed in the crystals. The gradual increase in Ti4+ content in the crystals on its increase in raw materials provides valuable information and good foundation for future work.

Formation and structure of a soliton in an antiferroelectric liquid crystal in an electric field

The soliton structure in an antiferroelectric liquid crystal in an electric field is calculated in the discrete phenomenological Landau model for phase transitions. The anticlinic structure of the antiferroelectric crystal gives rise to nontrivial features of the soliton structure and the stability of the soliton. The soliton is topologically stable in a metastable state if the electric field is much higher than the field of antiferroelectric-helix unwinding. A structural transition with a step-like change in the orientation of molecules occurs as the soliton field varies. A peculiar soliton (synclinic pair) can be formed if the barrier between the anti- and ferroelectric structures is large. The calculation shows the possibility of a large electroclinic effect in the soliton, i.e., a variation in the molecular tilt angle in an electric field in the vicinity of the transition of the structure to the synclinic state.

Flux growth of La‐doped lead zirconate stannate titanate antiferroelectric crystals

AbstractRelaxor antiferroelectric single crystals lead lanthanum zirconate stannate titanate (PLZST) with the composition around the morphotropic phase boundary (MPB) have been grown by flux method using 50 wt% PbO‐PbF2‐B2O3 as a flux. The obtained crystals are light yellow in color. The XRD patterns revealed that the habitual faces of the obtained crystal are (001). The crystal morphology was studied and related to a layer growth mechanism controlled by two‐dimensional growth. The chemical composition of as‐grown crystal was analyzed by inductively coupled plasma atomic emission spectrometry (ICP), indicating a slight decrease of the amount of Ti compared to the starting materials. The result was verified by the XRD patterns with the phase transformation from the co‐existence of tetragonal and rhombohedra phases to the single tetragonal phase. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Elastic and anelastic anomalies in (Ca,Sr)TiO 3 perovskites: Analogue behaviour for silicate perovskites

Values of bulk modulus ( K), shear modulus ( G) and mechanical quality factor ( Q) have been determined for polycrystalline samples across the CaTiO 3 (CST0)–SrTiO 3 (CST100) solid solution by resonant ultrasound spectroscopy. Because of similarities with low frequency elastic and anelastic anomalies due to twin wall motion reported in previous studies, a working hypothesis is developed in which dissipation processes are interpreted in terms of twin wall displacements. At high temperatures in CST50 the stability field of the I4/ mcm structure is marked by the disappearance of all resonance peaks (superattenuation). This is attributed to anelastic domain wall sliding. At room temperature the I4/ mcm phase of CST70 and CST80 has values of G which are lower than those of cubic or orthorhombic phases, and a concomitant drop in Q is interpreted as implying that the domain wall pinning process reported elsewhere to occur below ∼400–450 K is only partial. A similar drop in G and Q was found in CST95 below the P m 3 ¯ m ↔ I 4 / m c m transition at ∼238 K. The I4/ mcm ↔ Pbcm transition in CST70 at ∼230 K is marked by an abrupt increase in Q, suggesting that mobile twins in crystals with the I4/ mcm structure become effectively immobile in antiferroelectric crystals with the Pbcm structure. The I4/ mcm ↔ Pnma transition in CST50 is marked by a similarly abrupt increase in Q, consistent with twin walls becoming effectively immobile also in crystals with the Pnma structure. A fall in Q below ∼800 K in CST0, however, could imply that a degree of twin wall mobility might develop in Pnma crystals if the tetragonal spontaneous strain departs significantly from zero. The remarkable attenuation behaviour of crystals with the I4/ mcm structure at the relatively low stress conditions which apply during resonances of a parallelepiped with edge dimensions of ∼2–4 mm, is consistent with the view that a characteristic signature for tetragonal CaSiO 3 in the Earth's lower mantle should be a marked attenuation of seismic waves.

Antiferroelectric hysteresis loops with two exchange constants using the two dimensional Ising model

Monte-Carlo simulations are carried out to reproduce hysteresis loops of antiferroelectric single crystals using an Ising Hamiltonian in two dimensions where pseudospin interactions are defined by two constants. It is shown that with this approach, hysteresis loops can be obtained in very good qualitative agreement with the experiments. While our approach is similar to that of Milhazes et al. [Phys. Status Solidi B 242, 1141 (2005)], we also demonstrate that the hysteresis loop shapes heavily depend on the ratio of the electrostaticlike term to the intrinsic Hamiltonian of the system.

An aspect on relaxor behaviours and phase boundaries in ferroelectric mixed crystals

In order to search for Pb-free relaxor substances and to define relaxor behaviour, a theoretical aspect is presented from not only microscopic but also phenomenological viewpoint. In order–disorder type mixed crystals, the microscopic approach is attempted under conditions similar to those for relaxor perovskite-type oxides. Basing on the theory for the precursor to glass state, two kinds of technique of X-ray diffuse scattering (static properties) and quadrupole perturbed nuclear magnetic resonance (NMR-NQR) (dynamic properties) are discussed in ferroelectric (FE) -- antiferroelectric (AFE) mixed crystals of Rb1−x(NH4)xH2PO4. After investigating both boundary regions between FE and glass (G) phases, and between AFE and G phases, relaxor-like behaviours as a large dispersion in dielectric constants are found in the AFE-G phase boundary region where the gradual growth of wave number to make the energy minimum and a discontinuous broad NMR-NQR spectrum appear in quite different forms from those of the FE-G phase boundary region. On the other hand, in perovskite-oxides, the conditions for relaxor appearance are discussed within the phenomenological theory by comparing with the microscopic analysis in hydrogen-bonded systems.

Investigation on the nucleation kinetics of antiferroelectric ADP admixtured ferroelectric TGS crystals

Induction period and interfacial energy have been determined for the aqueous solution growth of ammonium dihydrogen orthophosphate admixtured triglycine sulphate. It is observed that the induction period decreases exponentially with supersaturation and hence the nucleation rate increases with the increase of supersaturation. The solubility of synthesized ADPTGS has been estimated at different temperatures. ADPTGS has a positive temperature coefficient of solubility. Nucleation parameters such as radius of the critical nucleus, number of molecules in the critical nucleus and critical free energy change have also been investigated.

Ferroelectric and Antiferroelectric Liquid Crystals

Ferroelectric liquid crystals have been a major research topic since 30 years. However, when it comes to liquid crystals, the term “ferroelectric” is strongly ambiguous and frequently not only leads to confusion and misunderstanding but also obscures the basic concepts. The property of ferroelectricity in liquid crystals was first claimed in 1975. Five years later so-called surface-stabilized ferroelectric liquid crystals were described, which caused a surge in industrial interest because of their promising electro-optical applications, in particular for high-resolution liquid crystal displays. The industrial interest led to a considerable activity in synthesizing new compounds with the desired properties. In the course of this materials development antiferroelectricity in liquid crystals was then also sought for and was finally identified in 1989. At the same time as the first industrial ferroelectric devices (the Canon displays) came on the market in 1995, the antiferroelectric liquid crystals were being considered as even more promising for applications. In parallel, ferrielectric liquid crystal materials were announced. Moreover, in 1995, a new phenomenon, the “thresholdless antiferro-electricity” was advertised. I believe that these names indicate a certain lack of comfort in adopting terms and definitions taken from the field of solid state phenomena. Therefore, it might be adequate to question whether liquid crystal materials really qualify to be called “ferroelectric, anti-ferroelectric and ferrielectric.” My own answer to this is to an important part negative. At least, no liquid crystal so far is ferroelectric. I will review our current understanding of polar liquid crystals and contrast them to ferroelectric and antiferroelectric solid crystals. While some of the electric properties can be very similar, it is the optical properties that really make the liquid crystals interesting. In particular, the optical properties of antiferroelectric liquid crystals are surprisingly rich, as discovered only in the very last years.

Phases Coexistence of Hydrogen-Bonded Mixed Ferroelectric and Antiferroelectric Crystals

The problem proton-glass and ferroelectric phases coexistence in Rb1−x (NH4) x H2AsO4 (RADA) and K1−x (NH4) x H2PO4 (KADP) crystals based on dielectric studies up to temperature 0.3 K is presented. The measurements were performed in the helium-3 cryostat in the temperature range from 300 K to 0.3 K. Glass behavior for the RADA is present even for a small concentration x = 0.01, whereas for the KADP the proton glass occurs for a concentration x > 0.05. The partial phase diagrams of RADP and KADP as a function of fractional ammonium concentration x and temperature T are presented.

Relaxor Behaviors in Ferroelectric-Antiferroelectric Mixed Crystals

In order to search for relaxor ferroelectrics or relaxor antiferroelectrics in Pb-excluded substances, ferroelectric and antiferroelectric mixed crystals Rb1-x(NH4)xH2PO4 are investigated from the theoretical viewpoint of the precursor to glass state. Both boundary regions between ferroelectric (FE) and glassy (G) phases, and between antiferroelectric (AFE) and glassy (G) phases are examined and relaxor-like behaviors are found in the present theory on X-ray diffraction and on dielectric constants. The relaxor-like behavior as an embryo of the glass is proposed in the antiferroelectric-glass (AFE-G) phase boundary region where the growth of glass ordering is shown in quite a different pattern from that of the FE-G phase boundary region. The condition for appearance of the relaxor is discussed as being due to the proton spatial correlation in structurally frustrated systems.

Staggered and Homogeneous Susceptibilities in NH 4 H 2 PO 4 -Type Anti-Ferroelectric Crystal

The cluster variation method (CVM) is applied to the Ishibashi model for NH 4 H 2 PO 4 (ADP) of a typical hydrogen bonded anti-ferroelectric crystal in order to obtain the staggered and the uniform susceptibility over all temperature regions in equilibrium. The hysteresis phenomena of susceptibility versus temperature observed in experiments are also derived on the basis of local equilibrium in Landau type variational free energy by making use of the natural iteration method (NIM) for the CVM.