Antiferroelectric Lead Zirconate Research Articles

Study of AC electrical properties in multigrain antiferroelectric lead zirconate thin films

Antiferroelectric lead zirconate (PZ) thin films were deposited by excimer laser ablation technique on Pt-coated Si substrates. Antiferroelectric thin film compositions are potential candidates for high charge storage and microelectromechanical systems. The antiferroelectric nature in PZ thin films was confirmed by means of double hysteresis behaviour in polarisation vs. applied electric field and double butterfly response in capacitance vs. applied voltage measurements. The maximum spontaneous polarisation observed was 37 μC/cm 2 with zero remnant polarisation at an applied electric field of 225 kV/cm. PZ thin films showed a polycrystalline multigrain structure and detail comprehensive study of dielectric relaxation and ac electrical properties were carried out.

Backward switching phenomenon from field forced ferroelectric to antiferroelectric phases in antiferroelectric PbZrO3 thin films

Antiferroelectric materials (example: lead zirconate and modified lead zirconate stannate), in which a field-induced ferroelectric phase transition is feasible due to a small free energy difference between the ferroelectric and the antiferroelectric phases, are proven to be very good candidates for applications involving actuation and high charge storage devices. The property of reverse switching from the field-induced ferroelectric to antiferroelectric phases is studied as a function of temperature, applied electric field, and sample thickness in antiferroelectric lead zirconate thin films deposited by pulsed excimer laser ablation. The maximum released charge density was 22 μC/cm2 from a stored charge density of 36 μC/cm2 in a 0.55 μ thick lead zirconate thin film. This indicated that more than 60% of the stored charge could be released in less than 7 ns at room temperature for a field of 200 kV/cm. The content of net released charge was found to increase with increasing field strength, whereas with increasing temperature the released charge was found to decrease. Thickness-dependent studies on lead zirconate thin films showed that size effects relating to extrinsic and intrinsic pinning mechanisms controlled the released and induced charges through the intrinsic switching time. These results proved that antiferroelectric PZ thin films could be utilized in high-speed charge decoupling capacitors in microelectronics applications.

Antiferroelectric lead zirconate thin films by excimer laser ablation

Utilization of antiferroelectric thin films was proposed for high charge storage capacitors and transducer applications. The volume changes that are associated with the AFE⇒ FE and FE ⇒ AFE phases are high enough to use them in MEMs device technology. Lead zirconate was the first identified antiferroelectric compound with a reported dielectric phase transition temperature of ∼ 230°C. In this article, deposition of lead zirconate thin films by a pulsed excimer laser ablation technique is reported. The antiferroelectric nature of the lead zirconate thin films were confirmed by the presence of double hysteresis loop in polarization vs. applied electric field response as well as double butterfly behavior in capacitance vs. voltage characteristics. The variations in the polarization hysteresis with temperature were elucidated in detail. The switching times between the field induced FE and AFE phases (backward switching) were studied at various applied electric fields.

Antiferroelectric thin films for MEMs applications

Antiferroelectric compositions have many potential applications in energy conversion and microelectromechanical systems. Electric field induced phase transitions between ferroelectric and antiferroelectric phases were studied in antiferroelectric lead zirconate and modified lead zirconate titanate stannate family thin films for various smart system applications. Thin films of various antiferroelectric thin film compositions such as PbZrO3, Nb-and La-modified Lead Zirconate Titanate Stannate were processed by pulsed excimer laser ablation technique. Dielectric, hysteresis, pyroelectric and switching properties were studied in detail for a new generation of functional materials. A comparative study of functional properties is presented with these antiferroelectric compositions in comparison with the conventional ferroelectric compositions.

Preparation and properties of antiferroelectric lead zirconate thin films by chemical solution deposition

Polycrystalline lead zirconate (PZ) thin films were prepared by chemical solution deposition. Pb/Zr atomic ratios of our precursor solutions were 1.0/1 and 1.2/1, respectively. Single-phase perovskite PZ films were obtained after heat treatment at 600°C and 700°C for 1h. The PZ thin films deposited on Pt/Ti/SiO2/Si substrate exhibited a double hysteresis loop, indicating that electric-field-induced antiferroelectric to ferroelectric phase transformation occurred at room temperature. The dielectric constant and loss tangent at room temperature were 131 and 0.045, respectively.

Dielectric and dc electrical studies of antiferroelectric lead zirconate thin films

Antiferroelectric lead zirconate thin films were deposited using KrF (248 nm) excimer laser ablation technique. Utilization of antiferroelectric materials is proposed in high charge storage capacitors and microelectromechanical (MEMs) devices. The antiferroelectric nature of lead zirconate thin films was confirmed by the presence of double hysteresis behavior in polarization versus applied field response. By controlling the processing parameters, two types of microstructures evolved, namely columnar (or in-situ) and multi-grained (or ex-situ) in PZ thin films. The dielectric and electrical properties of the lead zirconate thin films were studied with respect to the processing parameters. Analysis on charge transport mechanism, using space charge limited conduction phenomenon, showed the presence of both shallow and deep trap sites in the PZ thin films. The estimated shallow trap energies were 0.448 and 0.491 eV for in-situ and ex-situ films, with respective concentrations of ≈7.9×10 18/cc and ≈2.97×10 18/cc. The deep trap energies with concentrations were 1.83 eV with 1.4×10 16/cc for ex-situ and 1.76 eV with 3.8×10 16/cc for in-situ PZ thin films, respectively. These activation energies were found to be consistent with the analysis from Arrhenius plots of dc current densities.

Alternating current electrical properties of antiferroelectric lead zirconate thin films by pulsed excimer laser ablation

In situ crystalline lead zirconate (PZ) thin films were deposited on platinum metallized silicon substrates, using a 248 nm KrF pulsed excimer laser ablation technique. The antiferroelectricity in PZ thin films was confirmed by means of P vs E and C vs V measurements. The maximum observed saturated polarization (Ps) was 44 μC/cm2 at an applied field of 200 kV/cm. The calculated forward and backward switching fields were 71 and 154 kV/cm, respectively. The dielectric phase transition temperature was at ∼219 °C with zero dc bias and was increased to 290 °C in the presence of 4 V dc bias. Detailed comprehensive study was done on PZ thin films to understand the charge carrier transport with respect to frequency domain of dielectric and ac conductivity measurements. Effect of simultaneous dc bias on the frequency response of the dielectric dispersion and ac conductivity studies were done to understand the nature of charge carrier transport and their activation energies. The calculated activation energies, from ac conductivity and conductance measurements, in the absence of external dc bias were 0.42 and 0.37 eV, respectively. Measurements with the simultaneous application of 4 V dc bias gave two activation energy values 0.38 and 1.76 eV, respectively. The lower and higher activation energies were attributed to the shallow and deep trap energies respectively.

Antiferroelectric PbZrO3 films prepared by sol-gel processing

Antiferroelectric lead zirconate films with different thicknesses (0.3 to ≈ 1 μm) were prepared by the sol-gel method. The films were deposited on Pt/TiO2/Si and TiO2/Pt/TiO2/SiO2/Si substrates using a spin coating process. The preferred orientation and the perovskite phase content of the films were studied using X-ray diffraction analysis (XRD). Scanning electron microscopy (SEM) was used for microstructural characterization of the films. Dielectric properties were measured as a function of the temperature and frequency. Antiferroelectricity in the films was confirmed by dielectric double hysteresis loops at room temperature. The influence of precursor and processing parameters on cracking tendency and electrical characteristics of the sol-gel derived lead zirconate films were investigated.

Electrical fatigue of ferroelectric PbZr 0.5Ti 0.5O 3 and antiferroelectric PbZrO 3 thin films

The electrical fatigue of sol-gel derived ferroelectric lead zirconate titanate (PZT 50/50) and antiferroelectric lead zirconate (PZ) thin films was found to strongly depend on the orientation and morphology. Compared to the PZT films, the PZ thin films showed a much slower degradation of polarization, due to their having less internal stress during 180° domain switching of the antiferroelectric phase. More than 70% of the initial polarization value of PZ thin films was maintained after 10 9 cycles of 15 V bipolar square pulse. The randomly oriented PZT films showed less degradation of polarization, compared to the (111) preferred PZT films. In the PZ thin films, the rosette structure with a large portion of pyrochlore phase caused severe fatigue because of nonuniform distribution of electric field and internal stress.

Growth and study of antiferroelectric lead zirconate thin films by pulsed laser ablation

Antiferroelectric lead zirconate (PZ) thin films were deposited by pulsed laser ablation on platinum-coated silicon substrates. Films showed a polycrystalline pervoskite structure upon annealing at 650 °C for 5–10 min. Dielectric properties were investigated as a function of temperature and frequency. The dielectric constant of PZ films was 220 at 100 kHz with a dissipation factor of 0.03. The electric field induced transformation from the antiferroelectric phase to the ferroelectric phase was observed through the polarization change, using a Sawyer–Tower circuit. The maximum polarization value obtained was 40 μC/cm2. The average fields to excite the ferroelectric state, and to reverse to the antiferroelectric state were 71 and 140 kV/cm, respectively. The field induced switching was also observed through double maxima in capacitance–voltage characteristics. Leakage current was studied in terms of current versus time and current versus voltage measurements. A leakage current density of 5×10−7 A/cm2 at 3 V, for a film of 0.7 μm thickness, was noted at room temperature. The trap mechanism was investigated in detail in lead zirconate thin films based upon a space charge limited conduction mechanism. The films showed a backward switching time of less than 90 ns at room temperature.

Effect of substituents with different valences on antiferroelectric stability of antiferroelectric lead zirconate ceramics

The effect of lower valent substituents on the stability of the antiferroelectric phase of lead zirconate was studied by dielectric spectroscopy, Sawyer–Tower polarization methods, and electron diffraction techniques. The stability of an intermediate ferroelectric phase region was found to be enhanced with increasing lower valent substitution concentration. The influences of substituents of different ionic size and valence on the stabilization of the intermediate ferroelectric phase were differentiated. In general, lower valent substituents, such as K+ and Fe3+ affected antiferroelectric phase stability more significantly than higher valent ones.

Antiferroelectric lead zirconate thin films by pulsed laser ablation

Lead Zirconate (PbZrO 3) thin films were deposited by pulsed laser ablation method. Pseudocubic (110) oriented in-situ films were grown at low pressure. The field enforced anti-ferroelectric (AFE) to ferroelectric (FE) phase transformation behaviour was investigated by means of a modified Sawyer Tower circuit as well as capacitance versus applied voltage measurements. The maximum polarisation obtained was 36 μC cm −2 and the critical field to induce ferroelectric state and to reverse the antiferroelectric states were 65 and 90 kV cm −1 respectively. The dielectric properties were investigated as a function of frequency and temperature. The dielectric constant of the AFE lead zirconate thin film was 190 at 100 kHz which is more than the bulk ceramic value (120) with a dissipation factor of less than 0.07. The polarisation switching kinetics of the antiferroelectric PbZrO 3 thin films showed that the switching time to be around 275 ns between antipolar state to polar states.

Uniaxial stress and temperature dependence of field induced strains in antiferroelectric lead zirconate titanate stannat ceramics

The electric field induced antiferroelectric–ferroelectric phase transformation of polycrystalline lead zirconate titanate stannate (PZST) was investigated under prestress conditions at various temperatures. Lanthanum- and niobium-modified compositions of PZST with varying titanium content were prepared. The field induced strains of the ceramics were studied. The measured hysteresis loops indicate that the antiferroelectric–ferroelectric phase transformation depends on temperature, as well as on mechanical stress. For example compositions of niobium-modified PZST, which are in a ferroelectric state without pressure, can be transformed progressively into an antiferroelectric phase, by a pressure up to 30 MPa. Antiferroelectric compositions of both Lanthanum and Niob modified PZST can show either increasing or decreasing strain under the influence of a compressive stress. This depends on the composition of the sample and the strength of the pre-stress.

Electronic valency effect on the stabilization of ferroelectric phase in K1+ modified antiferroelectric lead zirconate

A comparative study was made on the lower valent K modified lead zirconate (PZ) and isovalent Ba modified PZ in terms of dielectric response, polarization hysteresis and electron microscopy. It was revealed for the first time that ionic size difference is not the only dominant factor in determining antiferroelectric-ferroelectric stability. Lower valency consideration could also enhance ferroelectricity in antiferroelectric PZ.

Incommensurately Modulated Polar Structures in Antiferroelectric Tin‐Modified Lead Zirconate Titanate: II, Dependence of Structure‐Property Relations on Tin Content

Studies of the structure‐property relations in Pb0.98Nb0.02‐ [(Zr1‐xSnx)0.97Ti3]1‐zO3 (PZST x/3/2) were performed for 0 < x < 0.50 by transmission electron microscopy, dielectric spectroscopy, and electrically induced polarization and strain methods. As the tin content increased, a general sequence of changes in phase stability was observed, including (i) a ferroelectric rhombohedral (FEr) phase (x < 0.15), (ii) a coexistence of FEr and antiferroelectric incommensurate (AFEin) states (x = 0.15), and (iii) an AFEin state (x > 0.15). Evidence will be presented that incommensurately modulated structures become pinned into long‐lived metastable states by quenched tin impurities, rather than evolving toward a commensurate phase. Maximum electrically induced strains (epsilon) and polarizations (P) were found in the compositional range of x similar/congruent 0.15, where FEr and AFEin regions coexisted. Values of epsilon as large as 0.5% were found at field strengths of <80 kV/cm. In addition, these studies demonstrated evidence for two electrically induced phase transitions (x = 0.15): (i) an antiferroelectric‐ferroelectric (AFE‐FE) transition near 40 kV/cm, and (ii) a secondary ferroelectric‐ferroelectric (FE‐FE) transition near 60‐80 kV/cm. The dominate contribution to epsilon was associated with the secondary transition, whereas the dominate contribution to P was associated with the first. For x < 0.15, evidence of an induced FE‐FE transition was found. For x > 0.15, an induced AFE‐FE transition was evident. However, no indications of a secondary FE‐FE transition were observed. Large epsilon values were not induced until field levels significantly greater than that required to induced polarization saturation were obtained, which indicates a decoupling of epsilon and P.

Properties and Orientation of Antiferroelectric Lead Zirconate Thin Films Grown by MOCVD

AbstractSingle-phase polycrystalline PbZrO3 (PZ) thin films, 3000-6000 A thick, have been grown by metal-organic chemical vapor deposition (MOCVD) on (111)Pt/Ti/SiO2/Si substrates at ≍525°C. X-ray diffraction analysis indicated that the PZ films grown on (111)Pt/Ti/SiO2/Si (Pt/Tgi/Si) showed preferred pseudocubic (110) orientation. In contrast, PZ films grown on 150 A thick PbTiO3 (PT) template layers exhibited a pseudocubic (100) preferred orientation, and PZ films deposited on TiO2 template layers consisted of randomly oriented grains. The PZ films grown on Pt/Ti/Si with or without templates exhibited dielectric constants of 120-200 and loss tangents of 0.01-0.0. The PZ films with (110) orientation exhibited an electric-field-inducedtransformation from the antiferroelectric phase to the ferroelectric phase with a polarization of ≍34 µC/cm2, and the energy that was stored during switching was 7.1 J/cm3. The field needed to excite the ferroelectric state and that needed to revert to the antiferroelectric state were 50 and 250 kV/cm, respectively. Relationships between the MOCVD processing and the film microstructure and properties are discussed.

Sol-gel fabrication of nanocomposites: Alternate thin layers of PbTiO 3 and PbZrO 3

Ferroelectric lead titanate and lead zirconium titanate, antiferroelectric lead zirconate, and alternatively deposited lead titanate-lead zirconate films have been fabricated by the sol-gel method. All the films were crystallized into perovskite structure by annealing at 650 °C or 700 °C for 30 min. Properties of the films coated onto platinized silicon substrate were examined by XRD and SEM. Variation of dielectric constant and loss, hysteresis behavior, and I-V characteristics were measured for pure and alternatively deposited nanocomposite films in order to investigate the role of the alternatively deposited nanocomposite films on structural and electrical properties. The decrease in leakage current density of PT-PZ nanocomposite film with PT as the first and PZ as the second layer was 10 to 100 times lower than that of PT, PZ, Or PZT film.

Structural and electrical properties of antiferroelectric lead zirconate thin films prepared by reactive magnetron co-sputtering

The structural and electrical properties of antiferroelectric lead zirconate thin films were investigated. The films were prepared by a reactive magnetron co-sputtering method followed by rapid thermal annealing. The crystallized films showed (240) preferred orientation on platinum-coated silicon substrates. The lead content in the films was found to affect the crystallization temperatures, the preferred orientation, the film morphology and the electrical properties. In particular, the hysteresis behaviour is sensitive to the amount of lead. The electric field forced transformation from the antiferroelectric phase to the ferroelectric phase was very similar to that observed in single crystals at room temperature, with a maximum polarization value of 70 μC cm-2. The average field required to excite the ferroelectric state and that for reversion to the antiferroelectric state were 290 kV cm-1 and 180 kV cm-1 respectively. The dielectric constant was 200 with an associated loss of 0.05 at 1 MHz. The Curie temperature was 248 °C at 1 kHz. The conduction mechanism of the films was similar to that observed for lead zirconate titanate films.

Optical Study of Domains in Antiferroelectric Ceramics

Antiferroelectric ceramics are now highly focused as giant strain actuator materials. In this study, domain formation in antiferroelectric lead zirconate based ceramics (Pb0.99Nb0.02[(Zr0.6Sn0.4)1-yTiy]0.98O3) was observed dynamically under an electric field at various temperatures using a high-resolution charge-coupled-device (CCD) microscope system. Field induced polarization and field induced strain were also measured. No domain was observed without an electric field, but clear domains appeared with an electric field due to the phase transition from an antiferroelectric to a ferroelectric state. Results of the optical study can explain well the electrical properties. The behavior of the field induced domains showed a shape memory effect and the domains were well oriented compared with normal ferroelectric ceramics.

Behaviour of a polar relaxation mode around the phase transition point in the antiferroelectric single crystal

In measurements of the dielectric dispersion carried out on single crystals of antiferroelectric lead zirconate a polar relaxation mode in the frequency range from to has been found. Using the Cole - Cole relation for the complex response the relaxation frequency and dielectric step of the mode have been determined as functions of temperature. In the paraelectric phase the squared relaxation frequency well obeys a relation with . The temperature dependence of the dielectric step corresponds to a sharp anomaly of the dielectric permittivity observed at the phase transition between the paraelectric and antiferroelectric states in . The phase transition mechanism of order - disorder type is discussed considering a disorder of the Pb sublattice in the paraelectric phase. It should be pointed out that similar dipolar relaxation in perovskites is known to appear only in those with ferroelectric properties.