David A. Payne

THE ROLE OF INTERFACES ON AN APPARENT GRAIN SIZE EFFECT ON THE DIELECTRIC PROPERTIES FOR FERROELECTRIC BARIUM TITANATE CERAMICS

Abstract We report the effect of interfaces (and thus internal surface area effects) on the value of dielectric constant (K′) calculated from capacitance and geometry data for sub-micron barium titanate (BaTiO3) ceramics prepared with decreasing grain size (and grain volumes). A series model is proposed to explain the decreasing values of apparent K′ obtained for grain sizes below 0.5 μm. A distinction is made between the true dielectric constant (K′) and the apparent dielectric constant (K′) calculated from experimental data. The progressive suppression in K′ is explained in terms of ferroelectric grains of constant dielectric constant (K′1) separated by a lower-K 2 boundary region (i.e., grain boundary) of constant thickness (d 2). The problem is one of an increasing interfacial surface area to grain volume ratio in fine-grain dielectrics. We begin by reporting original dielectric data for high pressure-densified ultrafine-grain BaTiO3 ceramics. Chemically prepared BaTiO3 powder was consolidated at high...

The effects of microstructure on the electrocaloric properties of Pb(Zr,Sn,Ti)O3 ceramics

Abstract When an electric field is applied to a dielectric material under adiabatic conditions there is a resultant change in temperature, a phenomenon known as the electrocaloric effect. Compositions in the Pb(Zr,Sn,Ti)O3 system (PZST) have several phases of nearly equal free energy, allowing antiferroelectric (AFE) to ferroelectric (FE) and paraelectric (PE) to ferroelectric (FE) transitions to occur. Data are presented for electrocaloric measurements on AFE materials in the vicinity of the Curie point. The effect of microstructure is reported, and experimental values are related to dielectric properties through thermodynamic relations. Culmination of this work resulted in the largest electrocaloric effect (2.6°K) measured to date for coarse grain material in the PZST system.

Thin-film ferroelectrics of PZT of sol-gel processing

The ferroelectric effect has been demonstrated for sol-gel derived lead zirconate titanate (PZT) (53/47) thin films. The respective values of coercive field and remanent polarization were 4*10/sup 6/ V/m and 0.36 C/m/sup 2/. The thin-film fabrication process is simple and compatible with Si planar technology, and offers a wide variety of potential uses for counting, memory, and integrated optical circuit applications.<<ETX>>

Nanocrystalline barium titanate: Evidence for the absence of ferroelectricity in sol‐gel derived thin‐layer capacitors

Nanocrystalline BaTiO3 thin‐layer capacitors were integrated onto silicon by sol‐gel processing using alkoxide precursor solutions. 200‐nm‐thick layers were formed and found to be comprised of 25‐nm grains in the cubic perovskite structure. Electrical measurements indicated a lack of polarization‐reversal hysteresis characteristics and Curie–Weiss behavior. The dielectric constant was 230 at room temperature. Properties are discussed in terms of a crystallite size effect. Stable dielectric properties with respect to temperature and voltage suggest that nanocrystalline BaTiO3 could find possible use as an integrated capacitor in decoupling and dynamic random access memory applications.

Improved stability for piezoelectric crystals grown in the lead indium niobate–lead magnesium niobate–lead titanate system

Higher coercive fields (EC) and depoling temperatures (TR∕T) were obtained for crystals in the Pb(In1∕2Nb1∕2)O3–Pb(Mg1∕3Nb2∕3)O3–PbTiO3 (PIN–PMN–PT) ternary system. Data are given for a crystal boule with starting composition 0.24PIN-0.44PMN-0.32PT, and with chemical distributions along the growth direction. The dielectric, piezoelectric, and elastic properties were determined. Similar to binary PMN–PT, ternary PIN–PMN–PT crystals have outstanding piezoelectric properties (e.g., d33∼900–1900pm∕V, k33∼0.83–0.92). In addition, PIN stabilizes piezoelectric performance by doubling EC (∼6kV∕cm) and increasing TR∕T by ∼20°C. These improvements are advantageous for acoustic transducers used in high-drive applications.

Preferred Orientations for Sol-Gel Derived Plzt Thin Layers

PLZT thin layers were deposited onto various substrates by sol-gel methods, and crystallized under different conditions and substrate treatments. Relationships are given for the chemical characteristics of the substrates surface and the preferred orientations which develop on heat treatment. A preferred (111) orientation always developed for perovskite crystallized on Pt layers which contained Ti on the surface. This was attributed to the formation of Pt 3 Ti and the role of heteroepitaxial nucleation and growth sites. In addition, a preferred (100) orientation was also obtained on unannealed Pt/Ti/SiO 2 /Si substrates which were free of Ti on the surface. This was attributed to self-textured growth with flat faces striving for minimum surface energy conditions. The results are discussed in terms of the importance of interfacial chemistry on the control of texture for crystallization of PLZT thin layers on coated substrates.

Antiferroelectric‐ferroelectric switching and induced strains for sol‐gel derived lead zirconate thin layers

Lead zirconate (PZ) thin layers were formed by a sol‐gel method and crystallized with a pseudocubic (111) or (100) preferred orientation. The field‐forced antiferroelectric (AFE)‐to‐ferroelectric (FE) phase transformation behavior was examined by Sawyer–Tower measurements. Dielectric properties were measured as a function of temperature and frequency, and the field‐induced transformational strain was measured by interferometry. Both the high‐field hysteresis behavior and the temperature‐dependent weak‐field dielectric properties were found to be strongly dependent on preferred orientation. An increase in the remanent polarization and dielectric constant was observed under high electric field strengths at room temperature, or for lower field strengths at higher temperature. Strains as large as 0.7% were determined for the field‐forced AFE‐to‐FE transformation. AFE‐to‐FE switching was demonstrated with full saturation at room temperature for high dielectric strength (100 MV/m) thin layers (300 nm).

Patterning of dielectric oxide thin layers by microcontact printing of self-assembled monolayers

This communication describes a technique used to pattern oxide thin layers using microcontact printing ({mu}CP) and sol-gel deposition. The technique involves {mu}CP of self-assembled monolayers (SAM`s) of alkylsiloxane on various substrates (SiO{sub 2}/Si, sapphire, ITO, and glass), followed by deposition of oxide thin layers from sol-gel precursors. Delamination of oxide layers from SAM-derivatized regions allows selective deposition of crystalline dielectric oxide layers on underivatized regions. To demonstrate the viability of this technique for integrated microelectronics and optics applications, patterned (Pb,La)TiO{sub 3} (PLT) and LiNbO{sub 3} layers were deposited on sapphire, silicon, and indium tin oxide (ITO) substrates. Use of lattice-matched substrates allows lithography-free deposition of patterned heteroepitaxial oxide layers. Strip waveguides of heteroepitaxial LiNbO{sub 3} with 4 {mu}m lateral dimensions were fabricated on sapphire. Dielectric measurements for patterned PLT thin layers on ITO are also reported. {copyright} {ital 1995} {ital Materials} {ital Research} {ital Society}.

Piezoelectric properties of sol‐gel‐derived ferroelectric and antiferroelectric thin layers

The piezoelectric properties of ferroelectric and antiferroelectric thin layers were investigated by interferometry as a function of frequency and dc electric bias. Materials included: a ferroelectric lead zirconate titanate (PZT) with a Zr/Ti ratio of 53/47; a relaxor ferroelectric La‐modified PZT with a Zr/Ti ratio of 70/30 and a La content of 7.8 at. %; and antiferroelectric lead zirconate. The hysteretic behavior of the piezoelectric coefficient due to polarization reversal was also studied. The layers were prepared by a sol‐gel method, and were found to have properties similar to bulk ceramics. Significant strain levels could be achieved in the materials due to the relatively high electric strengths supported in thin‐layer form. Polarization was found to be completely switchable between forward and reverse directions; however, the strain levels generated by switching were found to be inequivalent. In addition, pronounced piezoelectric relaxations and strong piezoelectric losses were observed.

Origins and evolution of stress development in sol-gel derived thin layers and multideposited coatings of lead titanate

Stress development in thin layers of lead titanate prepared by sol-gel processing was monitored by in situ laser reflectance measurements. Layers were spin coated onto silicon substrates and thermally cycled to 500 °C. The shrinkage normal to the rigid substrate was determined by in situ ellipsometry. Changes that occurred on drying and firing, which related to densification and stress development, are reported. The observed changes were explained in terms of evaporation and solvent/polymeric network interactions at lower temperatures, and thermal expansion mismatch between the substrate and the coating after formation of the dense oxide. Crystallization into the perovskite structure occurred only in thicker or multideposited coatings, altering the state of stress from tensile, to progressively more compressive, on cooling. The importance of the choice of substrate material, deposition method and heat treatment conditions, in relation to stress development and dependent electrical properties, are discussed.