Normal Ferroelectric Behavior Research Articles

Field Induced Dielectric Properties of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 Thin Films

ABSTRACTDC electric field induced dielectric properties of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) thin films were studied as a function of frequency at different temperatures. It was observed that the dielectric constant (ε) and dissipation factor (tanδ) were decreased in presence of bias field. The temperature of dielectric maxima was found to increase with increasing bias level. The low temperature (<Tm) frequency dispersion of dielectric permittivity was suppressed with the application of dc bias. After a certain bias voltage the relaxor property of films was disappeared i.e. the films exhibited normal ferroelectric behavior. Since the absence of long range interaction among the nanopolar clusters in PMN and its family is believed to be the origin of relaxor behavior, disappearance of relaxor nature in PMN-PT (70/30) films could be attributed to manifestation of long-range order at higher bias voltage. This was observed in the temperature dependence of dielectric constant i.e. the films neither exhibited any frequency dispersion in the temperature of dielectric maximum (Tm) nor showed any diffused phase transition. The relaxor property of PMN-PT thin films was studied in terms of diffused phase transition together with frequency dispersion of the temperature of dielectric maximum (Tm). Vogel-Fulcher relation was used to analyze the frequency dependence of temperature of dielectric maximum.

Rf-sputtering of PMNT thin films

We report on the realization of relaxor ferroelectric thin films by rf magnetron sputtering deposition. We investigated fabrication of films in the solid solution of PMN (Pb(Mg 1/3 Nb 2/3 )O 3 ) with PT (PbTiO 3 ). This material is the most studied among the relaxor ferroelectric family for applications in the field of microelectronics and microsystems. We chose the composition with 30% of PT, close to the morphotropic phase boundary between relaxor and normal ferroelectric behavior which exhibits good piezoelectric properties suited to actuators. We have grown the films in a cold deposition process. The substrates used were Si/SiO 2 coated by Ti/Pt electrodes. This allowed to synthesize pyrochlore-free PMNT ceramic thin films at temperatures between 450 and 675 °C in a post-deposition conventional annealing. We performed dielectric and ferroelectric characterizations of the films with Pt upper electrodes. Dielectric constant was measured as a function of temperature (up to 155 °C) and frequency (1 kHz 1 MHz). We obtained relative dielectric constant of the order of 1500. Relaxor behavior and ferroelectric properties are evidenced and are shown to be enhanced by annealing temperature.

Microstructural and ferroelectric properties of PbZr 1− xTi xO 3 thin films prepared by the polymeric precursor method

The polymeric precursor method was employed in the preparation of PZT thin films on Pt(111)Ti/SiO 2/Si(100) substrates. X-ray diffraction patterns revealed the polycrystalline nature of the PZT (53:47) thin films, which had a granular structure and a grain size of approximately 70 nm. A 350-nm thick film was obtained by running three cycles of the dip-coating/heating process. Atomic force microscopy (AFM) analyses showed the surface of these thin films to be smooth, dense and crack-free with low surface roughness (=2.0 nm). The PZT (53:47) thin films annealed at 700°C showed a well-saturated hysteresis loop. The C– V curves of perovskite thin film displayed normal ferroelectric behavior, while the remanent polarization (2 P r) and coercive field ( E c) of the film deposited and measured at room temperature were 40 μC/cm 2 and 110 kV/cm, respectively.

Crossover from relaxor to normal ferroelectric behaviour in (1− x)Pb(Mg 1/3Nb 2/3)O 3− xPbZrO 3 ceramic near x=0.5

Solid solutions of lead magnesium niobate and lead zirconate have been prepared by the conventional dry route. The dielectric spectroscopic technique has been used to study the temperature and frequency dependence of the relaxational behaviour. It is concluded from the temperature dependence of relaxation times that the system crosses over to the normal-ferroelectric regime near x=0.50, even though none of its two components is a normal ferroelectric.

Microstructure and electrical properties of perovskite (Pb, La)TiO3 thin film deposited at low temperature by the polymeric precursor method

High-quality (Pb, La)TiO3 ferroelectric thin films were successfully prepared on a Pt(111)/Ti/SiO2/Si(100) substrate for the first time by spin coating, using the polymeric precursor method. The X-ray diffraction patterns show that the films are polycrystalline in nature. This method allows for low temperature (500° C) synthesis, a high quality microstructure and superior dielectric properties. The effects on the microstructure and electrical properties were studied by changing the La content. The films annealed at 500°C have a single perovskite phase with only a tetragonal or pseudocubic structure. As the La content is increased, the dielectric constant of PLT thin films increases from 570 up to 1138 at room temperature. The C-V and P-E characteristics of perovskite thin films prepared at a low temperature show normal ferroelectric behavior, representing the ferroelectric switching property. The remanent polarization and coercive field of the films deposited decreased due to the transformation from the ferroelectric to the paraelectric phase with an increased La content.

Preparation and properties of ferroelectric Pb1-xCaxTiO3 thin films produced by the polymeric precursor method

Pb1 − x Ca x TiO3 thin films with x = 0.24 composition were prepared by the polymeric precursor method on Pt/Ti/SiO2/Si substrates. The surface morphology and crystal structure, and the ferroelectric and dielectric properties of the films were investigated. X-ray diffraction patterns of the films revealed their polycrystalline nature. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses showed the surface of these thin films to be smooth, dense and crack-free with low surface roughness. The multilayer Pb1 − x Ca x TO3 thin films were granular in structure with a grain size of approximately 60–70 nm. The dielectric constant and dissipation factor were, respectively, 174 and 0.04 at a 1 kHz frequency. The 600-nm thick film showed a current density leakage in the order of 10−7 A/cm2 in an electric field of about 51 kV/cm. The C-V characteristics of perovskite thin films showed normal ferroelectric behavior. The remanent polarization and coercive field for the deposited films were 15 μC/cm2 and 150 kV/cm, respectively.

Preparation and properties of ferroelectric BaTiO3 thin films produced by the polymeric precursor method

Pb1 − xCaxTiO3 thin films with x = 0.24 composition were prepared by the polymeric precursor method on Pt/Ti/SiO2/Si substrates. The surface morphology and crystal structure, and the ferroelectric and dielectric properties of the films were investigated. X-ray diffraction patterns of the films revealed their polycrystalline nature. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses showed the surface of these thin films to be smooth, dense and crack-free with low surface roughness. The multilayer Pb1 − xCaxTO3 thin films were granular in structure with a grain size of approximately 60–70 nm. The dielectric constant and dissipation factor were, respectively, 174 and 0.04 at a 1 kHz frequency. The 600-nm thick film showed a current density leakage in the order of 10−7 A/cm2 in an electric field of about 51 kV/cm. The C-V characteristics of perovskite thin films showed normal ferroelectric behavior. The remanent polarization and coercive field for the deposited films were 15 μC/cm2 and 150 kV/cm, respectively.

Study of the structure and dielectric relaxation behavior of Pb(Mg1/3Nb2/3)O3–PbTiO3 ferroelectric ceramics

(1–x)PMN–xPT[PMN, Pb(Mg1/3Nb2/3)O3; PT, PbTiO3] system ferroelectric ceramics with x = 0.30, 0.33, 0.35, and 0.38 were synthesized by the columbite precursor method. Their structure and dielectric behavior were investigated. X-ray diffraction results demonstrate that no two-phase region is presented, but a quasi-cubic to tetragonal phase boundary lies between x = 0.30 and 0.33. Examination of the dielectric behavior reveals that the transformation from relaxor to normal ferroelectric behavior across the morphotropic phase boundary (MPB) is successive and continuous. It is suggested that x 4 0.30 to 0.33 is the composition of MPB for the PMN–PT system. The MPB is also a boundary for the PMN–PT system to transform from relaxor to normal ferroelectrics.

Structural origin of relaxor ferroelectrics—revisited

Relaxor behavior of diffuse phase transition and large frequency dispersion is found among Pb-containing complex perovskites. With slightly different compositions or structures, these same complex perovskites also exhibit normal ferroelectric (FE) or antiferroelectric (AFE) behavior. The AFE transitions involve a volume decrease and are enhanced by increasing the size mismatch between ferroelectrically active B″ cations and ferroelectrically inactive B′ cations. This is in contrast to the FE transitions which involve a volume increase and are enhanced by enlarging the space available for ferroelectrically active B″ cations. In relaxors, the size of B′ cations is always larger than that of B″ cations, so an increase in the size mismatch is accompanied by a parallel increase in the molar volume. Therefore, a competition between AFE and FE couplings is always present. Such AFE/FE competition has an analogy in magnetism: the competition between antiferromagnets and ferromagnets gives rise to a spin glass behavior in the intermediate random alloys between antiferromagnets and ferromagnets. Evidence in support of this concept is found in the structural characteristics, transformation volumes, pressure dependencies, transition/depolarization temperatures, and phase diagrams of relaxors ferroelectrics and related compounds.

Chemical order in PMN-related relaxors: structure, stability, modification, and impact on properties

High temperature thermal treatments were used to modify the cation order in several tantalate and niobate members of the Pb(Mg 1/3Nb 2/3)O 3 (PMN) family of relaxors. The observation of complete 1:1 structural order in several compositions, and the refined cation occupancies of well-ordered samples conflict with the predictions of the “space charge” model, and support the “random site” description for the B-site order. In this charge balanced model one of the positions in the ordered structure is solely occupied by Ta (Nb), while the other contains a random distribution of Mg and the remaining Ta (Nb) cations. The stability of the order and magnitude of the domain growth is strongly influenced by solid solution additives. For Pb(Mg 1/3Ta 2/3)O 3 (PMT), ordering-enhancing Zr, Sc, or La substituents increase the cation order–disorder transition temperature (∼1375°C in pure PMT) and promote extensive domain coarsening. For pure PMN a low temperature (<1000°C) order–disorder transition prevents any structure modification, and domain growth could only be realized with additives (Tb, Sc, or La) that stabilize the order to temperatures where the samples are “kinetically active”. The retention of relaxor behavior in all the fully 1:1 ordered, large-domain PMT and PMN-based ceramics suggests that the disorder on the random site is critical in frustrating ferroelectric order. By systematically controlling the concentration of ferroelectrically active cations on this position in fully ordered (1− x)Pb(Mg 1/3Ta 2/3)O 3–( x)Pb(Sc 1/2Ta 1/2)O 3 solid solutions, a crossover from relaxor to normal ferroelectric behavior was induced at x=0.5.

Low temperature synthesis of PbTiO 3 thin films by MOCVD without carrier gas

A new MOCVD (metal–organic chemical vapor deposition) technique employing the precursor delivery without carrier gas was developed in the deposition of PbTiO 3 thin films, which enables low temperature (450°C) synthesis and high grow rates (∼6.0 μm/h). Substrates used were bare Si, TiO 2 buffered Si, and platinized Si. Tetraethyl lead, titanium tetra-isopropoxide, and oxygen were used as precursors. Perovskite PbTiO 3 thin films were successfully grown on all kinds of substrates investigated at the substrate temperature of 450°C. However, the C–V characteristics of perovskite thin films prepared at low temperature did not always show normal ferroelectric behavior. Without carrier gas, impinging of non-adsorbing species with substrates would be suppressed as much as possible. The difference in growth behaviors with or without carrier gas was compared with each other.

Controlling the Chemical Order in PMN-Type Relaxors

AbstractInvestigations of pure and chemically substituted tantalate and niobate members of the Pb(Mg1/3 Nb2/3)O3 (PMN) family of perovskite relaxors demonstrate that the degree of cation ordering and size of the chemically ordered domains can be extensively modified by thermal treatment. These observations and refinements of the cation occupancies in well ordered samples conflict with the predictions of the widely accepted “space charge model”, and instead support a “random site” model for the 1:1 B-site ordering. In this model one of the positions in the ordered structure is occupied by Ta (or Nb) and the other contains a random distribution of Mg and the remaining Ta cations. The stability of the order and magnitude of the domain growth can be enhanced by relatively small concentrations of selected solid solution additives (e.g. Zr in Pb(Mg1/3Ta2/3)O3 (PMT); Th or Sc in PMN). Correlations between the stability of the 1:1 order and the size of the solid solution additive can be used to understand the different responses of the cation order in PMN and PMT to thermal treatment. Results are also presented for the dielectric response of fully ordered relaxors in the (l–x) Pb(Mg1/3Ta2/3)O3 – (x) Pb(Sc1/2 Ta1/2)O3 system. While large domain samples of PMT-rich compositions exhibit a relaxor response, a crossover to normal ferroelectric behavior is observed for x = 0.5. The change in the dielectric response can be rationalized in terms of the effect of the chemistry of the random site sub-lattice on the correlation length of the ferroelectric coupling.

Correlation of freezing dynamics and domain-like states in relaxor ferroelectrics

Abstract Tetragonal PLZT ceramics (Zr/Ti = 40/60) with lanthanum contents of approximately 12 atomic% posses a unique transformation. Dielectric constant measurements have revealed a spontaneous switching between relaxor and normal ferroelectric behaviors, in addition significant thermal hysteresis effects were observed near the switching temperature. Temperature dependent x-ray line broadening above the switching temperature was observed which revealed the development of significant internal strain indicating the presence of local cubic-tetragonal structural transformations which preserve the average cubic symmetry, while line splitting was observed below the switching temperature indicating the formation of a macroscopic tetragonal structure. Micropolar domain coarsening and a subsequent transformation to a normal micron-size domain configuration was observed by hot-stage transmission electron microscopy.

Relationship between B-site order and properties in Pb(B′B″)O3perovskites

Abstract A simple classification scheme is presented which essentially relates the scale of B-site cation order in complex lead based perovskites Pb(B′B″)O3 with either normal ferroelectric (antiferroelectric) or relaxor ferroelectric behavior, as observed in these materials.

Classification and consequences of complex lead perovskite ferroelectrics with regard to B-site cation order

From a number of studies on ferroelectric and related materials based on complex lead perovskites [Pb(Bx′B1−x″)O3], it is apparent that the B-site cation order influences the crystallography, phase transitions, and other physical properties. A classification of complex lead perovskites is presented based on the relative scale of long-range cation order. In particular, we discuss the implications of cation order in relation to relaxor and normal ferroelectric behavior.

Evolution of ferroelectricity in ultrafine-grained Pb5Ge3O11 crystallized from the glass

By controlled crystallization of the ferroelectric crystalline phase of Pb5Ge3O11 from the glass of the same composition, the evolution of ferroelectric behavior has been studied as a function of grain size. The large-grained material (≳1 μm) exhibits normal ferroelectric behavior. However, during the initial growth of grains of about 10-nm dimensions the polarization is unstable and no dielectric anomaly is observed. The behavior of this fine-grained material can be understood in terms of large dipolar clusters which can be frozen into ferroelectriclike order at low temperatures in the presence of an electric field, but which are too small to stabilize spontaneous ferroelectric order.