Antiferroelectric Transition Temperature Research Articles

Dielectric properties and infrared spectra of Ag0·92Li0·08NbO3 ceramics

The dielectric properties of Ag0·92Li0·08NbO3 (ALN8) ceramics were investigated in a broad frequency range (20 Hz −90 THz). The dielectric spectra of ALN8 ceramics mainly are impacted by the electrical conductivity at higher temperatures (above 500 K) and low frequencies (below 1 MHz) and the contribution of the soft relaxation mode, which frequency is below 50 cm−1. The electrical conductivity has two anomalies close to antiferroelectric and ferroelectric phase transition temperatures, respectively. The most pronounced decrease of the activation energy is observed close to the ferroelectric phase transition temperature. The values of activation energies are typical for oxygen vacancies transport. Some phononic modes are slightly temperature dependent close to the ferroelectric phase transition temperature confirm the influence of Ag, Nb and Li ions dynamics on the phase transitions.

Magnetic Properties of NH4H2PO4 and KH2PO4: Emergence of Multiferroic Salts.

We observe sharp step-down discontinuities in the magnetic susceptibility of NH4H2PO4 and NH4H2PO4-d60 (60% deuterated) along the a- and c-axes occurring exactly at their antiferroelectric transition temperatures. For the case of KH2PO4, less pronounced discontinuities occur at the ferroelectric transition temperature. To explain this, we treat the acid protons as individual oscillators that generate current elements that translate to magnetic forces in near resonance with each other. With decreasing temperature, the resonant forces become more commensurate, which amplifies a disproportionate drop off of two types of magnetic forces to eventually trigger the structural phase transitions. For the case of NH4H2PO4, the associated internal magnetic field appears to aid the NH4+ to order at a higher temperature. At 49 K, a shoulder-like anomaly in both NH4H2PO4 and KH2PO4 is attributed to a possible onset of macroscopic quantum tunneling of protons. Our findings bring forth a new category of intrinsic multiferroic systems.

Electro-caloric behaviors of lead-free Bi0.5Na0.5TiO3-BaTiO3 ceramics

Electro-caloric (EC) properties of lead-free Ba0.5Na0.5TiO3-xBaTiO3 (BNT-xBT) ceramics prepared by citrate method are investigated at temperatures of 30–250°C. Based on thermodynamics calculations, BNT-xBT (x = 0, 0.05, 0.06, 0.1, 0.25, 0.3) are found to show EC effects different with other lead-based or lead-free ferroelectric ceramics, i.e., they absorb heats (refrigeration effect) during the processes of field application while other ferroelectric ceramics show refrigeration effect during the processes of field removal. The EC temperature change of BNT-xBT can be as large as 2.1°C under an electric field of 60 kV/cm, which is larger than most of the lead-free ferroelectric bulk ceramics. When x is close to the morphotropic phase boundary (x ~ 0.06–0.1), the EC temperature change of BNT-xBT shows a maximum near the ferroelectric to anti-ferroelectric transition temperature, which is characterized by dynamic mechanical analysis. This study suggests that these lead-free ferroelectric materials are promising in the practical application as EC coolers.

Temperature‐Dependent Electrical Properties of 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 Ceramics

Temperature‐dependent electrical properties of lead‐free 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 (BNT–BT) ceramics were investigated. Below 100°C, this rhombohedral–tetragonal morphotropic phase‐boundary composition shows dominant ferroelectric order with typical ferroelectric polarization–electric field (P(E)) loop and butterfly bipolar strain–electric (S(E)) curve. Antiferroelectric order tends to prevail when temperature reaches about 100°C, characterized by a pinched P(E) loop and altered bipolar S(E) butterfly. Near the ferroelectric–antiferroelectric transition temperature, the composition shows a giant bipolar and unipolar strain of 0.40% and 0.42%, respectively. The highest value of maximum strain divided by the applied field (i.e., Smax/Emax) reaches 700 pm/V at 100°C. With a further increase of temperature to 200°C, a slight decrease of the strain is observed. Especially, it is found that the hysteresis of the unipolar S(E) curve decreases with increasing temperature. These results may be helpful for further understanding and thus designing new BNT‐based lead‐free piezoelectric systems.

Antiferroelectric-ferroelectric phase transitions in Pb1−xBaxZrO3 ceramics: Effect of PbO content

The irreversibility of the antiferroelectric (AFE) to FE phase transition in Pb1−xBaxZrO3, x=0.75–0.1, compositions is shown to be a consequence of lattice vacancies arising from PbO evaporation during ceramic processing. Previously, the absence of a FE→AFE cooling transition was thought to be due to the transformational strain and the fragmentation of ferroelectric domains. Appropriate compensating levels of excess PbO added to starting powders generate the FE→AFE transition. For lower levels of Ba2+ substitution, x=0.05, the transition is reversible in noncompensated samples, but PbO compensation raises the FE→AFE transition temperature by ∼25°C.

Structures and phase transitions in some Pb2B′B″O6 complex perovskite-type compounds

In order to study the influence of substitutions and of the ionic radii of B’ ions on structure and phase transitions, we present some physical measurements and data on Pb2B′B″O6 (B”=W, Nb, Mo) complex perovskite compounds. By Mn and Fe substitution for Mg in Pb2MgWO6 compound a change in lattice parameters and shift of antiferroelectric transition temperature is observed. It appears that in all three series of compounds a linear dependence between ferroelectric or antiferroelectric transition temperature and B’ ionic radii is observed.

Calculation of phase diagrams for solid solutions of ferroelectrics

The integral equations for calculating ferroelectric and antiferroelectric phase transition temperatures, order parameters, and critical concentrations of solid solution components are derived. The electric dipoles randomly distributed in the system are treated as sources of random fields. The random field distribution function is constructed taking into account the contribution of nonlinear effects and the differences in the dipole orientations for different solid solution components. The dependence of the phase transition temperature on the composition of a binary solid solution in the ferroelectric-antiferroelectric and ferroelectric-paraelectric systems is calculated. Numerical calculations are carried out for the PbTixZr1−x O3 and BaZrxTi1−x O3 solid solutions. The results obtained are in good agreement with the experimental phase diagrams of these systems. Analysis of the results indicates that any solid solution containing ferroelectric (antiferroelectric) and paraelectric components transforms into a relaxor state at sufficiently high concentrations of the paraelectric component.

Phase diagram of mixed ferroelectrics

The integral equations for calculation of ferroelectric and antiferroelectric transition temperatures, order parameters and critical concentrations of mixed system components have been derived. The electric dipoles randomly distributed in mixed system were considered as random field sources. This field distribution function with nonlinear and spatial correlation effect contribution and with different orientations of the components electric dipoles has been written. The concentration dependence of A1−xBx mixed system transition temperature was calculated for the cases when A and B materials are antiferroelectric and ferroelectric respectively and when A and B materials are ferroelectric and paraelectric. The numerical calculation were carried out for PbTixZrxO3 and BaZrxTii-xO3. The obtained results describe rather good experimentally observed phase diagrams of these mixed systems. The physical reasons of strongly different behaviour of the systems (in particular the relaxor properties of BaZrxTi1−xO3 at x>0.25) and peculiar role of lead ions in appearance of ferroelectric and antiferroelectric phase transitions are discussed.

μ–H Interaction in Hydrogen Bonding Systems

Muon spin rotation (μSR) experiments were performed on single crystal samples of KH2PO4(KDP) and KD2PO4(dKDP) to study the dynamics of hydrogen in hydrogen bonding systems. At low temperature, the nuclear dipole interaction of muon and proton was confirmed from the angular dependence of precession frequency of the muon spin under zero magnetic field. The muon occupation site was also determined. A clear change in μSR spectra was observed at the antiferroelectric transition temperature (123 K). At 90 K well below the transition temperature, the muon spin starts to relax, possibly due to muon dynamics.

Calorimetric baseline fitting: Application to titanite

In order to analyse calorimetric measurements of a phase transition, it is necessary to determine the baseline from which the excess specific heat is measured. In this study, this baseline is determined by using the constraint that the resulting heat capacity anomaly must be consistent with measurements of the phase transition by other techniques. The method is particularly useful when other mechanisms make it difficult to predict the low-temperature behaviour of the baseline. Titanite provides an example of this, since the antiferroelectric transition temperature is close to the temperature at which the phonon contribution to the specific heat begins to fall rapidly.

The Isotope Effect in Hydrogen-Bonded Systems

The giant isotope effect on the ferro- and antiferroelectric transition temperature upon deuteration of hydrogen-bonded systems is well known experimentally since various decades. Yet, theoretically only recently a microscopic understanding of this effect has been achieved which, specifically, took into account the geometry of the O ⋯ H ⋯ O bond. The implications of this modeling are multiple as numerous hydrogen-bonded organic systems show the same effects as ferro- and antiferroelectrics, i.e., cooperative proton tunneling at a well-defined temperature.

Effect on Electrical Properties of Barium and Strontium Additions in the Lead Lanthanum Zirconate Stannate Titanate System

The effect of barium (Ba) and strontium (Sr) additions on the electrical properties of lead lanthanum zirconate stannate titanate (PLZST) ceramics and their electrically induced phase change behavior was examined. Sr additions decreased both the ferroelectric (FE) ↔ antiferroelectric (AFE) transition temperature (TAFE‐FE) and the temperature of the maximum dielectric constant (TMAX). This indicates that Sr additions stabilize the AFE phase. Along with B‐site modifications Sr additions can be used to decrease the switching field and hysteresis. Ba additions caused the temperature range of the AFE phase to narrow by increasing TAFE‐FE and decreasing TMAX. This behavior indicates an ability to lower the switching field and suppress hysteresis. Using a combination of both A‐site and B‐site modifications it is possible to tailor the properties (for example, switching field, hysteresis, and operating temperature range) of this group of phase change materials to meet the requirements of specific applications.

Antiferroelectric superstructures of Pb2MgWO6

Abstract The antiferroelectrk superstructures of Pb2MgWO6 were investigated by x-ray diffraction and transmission electron microscopy at various temperatures. The analysis of electron diffraction patterns revealed the existence of an intermediate phase in a narrow temperature range just below the well-known antiferroelectric transition temperature T c =39 °C. The superstructure of the low temperature phase is found to be modulated with superimposition of two independent modulation modes {110} p and {1/2 1/2 0} p . We will also discuss this lattice modulation in conjunction with well-known antiferroelectric structure of PbZrO3.

X-ray and electrical study of the phase transitions in (Pb1-xBax)(Yb1/2Nb1/2)O3

Abstract In order to study the effect caused by atomic substitution on the phase transition in Pb(Yb1/2Nb1/2)O3, crystallographic and dielectric properties of (Pb1-xBax)(Yb1/2Nb1/2)O3 ceramics system have been investigated for 0≤x≤0.5, as a function of temperature. A continuous series of solid solutions with ordered perovskite structure has been found. While the antiferroelectric transition temperature markedly decreases with increasing Ba concentration, the value of dielectric constant in the immediate vicinity of the peak is maximum at x=0.14. It has been revealed that the low symmetry phase changes from the antiferroelectric state to ferroelectric one near x=0.12. The antiferroelectric-paraelectric transition is relatively sharp for 0≤x≤0.1, but the ferroelectric-paraelectric transition is diffuse. A brief discussion of the effect caused by Ba substitution is given.

Effects of pressure, DC-electric field and frequency on the dielectric properties of lead indium niobate

Abstract The pressure (0–6kbar), DC-bias field(0–11kV/cm) and frequency(300Hz–100kHz) dependence of dielectric properties of PIN ceramics prepared by different thermal processing techniques (conventional method:sample A and fast firing;sample B) were reported. PIN sample A reveals coexistence of a ferroelectric relaxor (disordered state) and an antiferroelectric phase(ordered one), while sample B reveals a ferroelectric relaxor. For sample A, the permittivity maximum(erm′ =1800 at 1kHz) temperature Tm decreases with pressure(dTm/dp=−2°C/kbar) and antiferroelectric transition temperature Tt increases with p(dTt/dp=5°C/kbar). For sample B(with e rm′ = 3500 at 1kHz), the Tm decreases with dTm/dp=−3°C/kbar, and a remarkable decrease in e rm′ with DC-bias field and a strong dielectric relaxation of polydispersive type which obeys the Cole-Cole arc law were observed.

Comparative analysis of the antiferroelectric behaviour in C 4O 4H 2 and NH 4H 2PO 4

A comparative analysis of the macroscopic antiferroelectric parameters of C 4O 4H 2 (squaric acid) and NH 4H 2PO 4 (ADP) within the framework of the sublattice field approach leads to estimates of the respective dipole moments which in the former case can be compared with an estimate based on crystal structure data at T<T N (antiferroelectric transition temperature). The arrangement of the dipole moment is considerably larger in the case of squaric acid.

Ionic rearrangements and domain growth near antiferroelectric transitions: EPR study of NH4H2AsO4, ND4D2AsO4, NH4H2PO4, and ND4D2PO4

Using electron paramagnetic resonance spectroscopy we have measured the temperature dependence of ionic rearrangements and domain nucleation around the antiferroelectric transition temperature Tc of NH4H2AsO4, ND4D2AsO4, NH4H2PO4, and ND4D2PO4. CrO43− radicals, produced by γ-irradiation of K2CrO4-doped samples, were used as microscopic probes because their charge, size, and symmetry match those of the host anions. The use of high deuteration level and "monodomain" samples prepared by temperature cycling was found to be crucial in the signal assignment and line-shape analysis. The results show that as a sample approaches Tc from T &gt; Tc, the hydrogen-bonded protons slow down anomalously, much more slowly than expected for Arrhenius behaviour. Simultaneously, the lattices develop "clusters" of antiferroelectrically ordered molecules. These clusters eventually [Formula: see text] expand to occupy the whole lattice and thus complete the lattice ordering. The probe selection and sample preparation methodology discussed and the microscopic details of the ionic rearrangements reported appear to be highly significant for further studies of these phase transitions.

Dynamical studies of highly deuterated betaine phosphate near the antiferroelectric phase transition

The dielectric response and the Raman spectra of single crystals of deuterated betaine phosphate are studied around the antiferroelectric phase transition. The dielectric data between 10 MHz and 11 GHz can be explained on the basis of a simple Debye-relaxation with a critical slowing-down of the relaxation rate on approachingT C . Using the Cole-Davidson form of the dielectric function we succeeded in fitting the data in the whole frequency range from 10 MHz to 11 GHz and from 64–400 GHz over a temperature range from 145–280 K. Raman spectra clearly indicate that the doubling of the unit cell does not take place at the antiferroelectric transition temperature, but some degrees below.

Pressure and temperature dependence of dielectric properties of Pb(Mg1/2W1/2)O3

The dielectric properties such as the permittivity, epsilon , and the dielectric loss tangent, tan delta , of Pb(Mg1/2W1/2)O3 were measured at various pressures up to 8 kbar. The permittivity epsilon obeys the Curie-Weiss law in the paraelectric phase at constant pressure. With increasing pressure p, the antiferroelectric transition temperature Tn decreases with a pressure coefficient dTn/dp=-3.8+or-0.2K kbar-1, the extrapolated Curie-Weiss temperature T0 increases with a pressure coefficient dT0/dp=1.4+or-0.2K kbar-1, the Curie constant C decreases at a rate of about 3.9% kbar-1, and the maximum value of epsilon , epsilon max, is almost constant at pressures below 4 kbar and then increases. The increase in epsilon max with p is associated with the decrease in the difference Delta T(=Tn-T0) with p. with increasing p, the difference Delta T decreases and extrapolates to zero at the pressure pt of about 18 kbar. At this pressure pt, the change from the antiferroelectric transition to the ferroelectric one is expected. At constant temperature, the pressure dependence of epsilon can be represented by a Curie-Weiss-like relationship expressed in terms of pressure: epsilon = epsilon 0*+C*/(p-p0). Both constants C* and p0 are functions of temperature. The dielectric properties associated with the antiferroelectric transition are interpreted in terms of a phenomenological theory.

The Effect of the Hydrostatic Pressure on the Antiferroelectric Transition of Pb(Mg1/2W1/2)O3

The dielectric properties of Pb(Mg1/2W1/2)O3 were measured at various pressures up to 8 kbar. With increasing pressure p, the antiferroelectric transition temperature Tn decreases with dTn/dp=-3.8±0.2°C/kbar, the extrapolated Curie-Weiss temperature T0 increases with dT0/dp=1.4±0.2°C/kbar, and the maximum value of the permittivity ε, εmax, is almost constant below 4 kbar and then increases. This increase in εmax with p is associated with the decrease in the difference ΔT(=Tn-T0) with p. The ΔT extrapolates to zero at pt≈18 kbar where the change from the antiferroelectric transition to the ferroelectric one is expected. The dielectric properties are interpreted in terms of a phenomenological theory.