I. M. Reaney

Effect of Structural-Changes in Complex Perovskites on the Temperature-Coefficient of the Relative Permittivity

The dielectric behavior and structure of the Sr(Zn1/3Nb2/3)O3‐Ba(Zn1/3Nb2/3)O3 solid solution have been investigated with the intention of understanding the relationship between the structural changes and the temperature coefficient of the relative permittivity τe. A correlation between the value of τe and the occurrence of O‐octahedra tilts has been established. The occurrence of ferroelastic domains and their influence on τe has also been investigated. It is proposed that the results obtained can be used to generalize about the structure‐property relationships in compounds of the same class.

Orientation of rapid thermally annealed lead zirconate titanate thin films on (111) Pt substrates

The nucleation, growth, and orientation of lead zirconate titanate thin films prepared from organometallic precursor solutions by spin coating on (111) oriented platinum substrates and crystallized by rapid thermal annealing was investigated. The effects of pyrolysis temperature, post-pyrolysis thermal treatments, and excess lead addition are reported. The use of post-pyrolysis oxygen anneals at temperatures in the regime of 350-450 degrees C was found to strongly affect the kinetics of subsequent amorphous-pyrochlore-perovskite crystallization by rapid thermal annealing. The use of such post-pyrolysis anneals allowed films of reproducible microstructure and textures [both (100) and (111)] to be prepared by rapid thermal annealing. It is proposed that such anneals and pyrolysis temperature affect the oxygen concentration/average Pb valence in the amorphous films prior to annealing. Such changes in the Pb valence state then affect the stability of the transient pyrochlore phase and thus the kinetics of perovskite crystallization.

Investigation of Pt/Ti bilayer metallization on silicon for ferroelectric thin film integration

The stabilities of Pt/Ti bilayer metallizations in an oxidizing atmosphere have been investigated with several thicknesses of interfacial Ti‐bonding layers. Reactions in the Pt/Ti/SiO2/Si interface were examined as a function of various annealing conditions in the temperature range 200–800u2009°C by using Rutherford backscattering spectrometry, Auger electron spectroscopy, x‐ray diffraction, and transmission electron microscopy. Thermal treatment in oxygen was found to cause rapid oxidation of the Ti layer, accompanied by the migration of Ti into the Pt film. Diffusion of oxygen through the Pt grain boundaries was mainly responsible for the adverse reactions at the interface and loss of mechanical integrity. Thin Ti (10 nm) layers resulted in the depletion of the interfacial bonding layer causing serious adhesion problems, whereas thicker Ti films (100 nm) caused the formation of TiO2−x in the Pt‐grain boundaries, ultimately encapsulating the Pt surface with an insulating TiO2 layer. Improved stability and ad...

Spontaneous (zero‐field) relaxor–to–ferroelectric‐phase transition in disordered Pb(Sc1/2Nb1/2)O3

Recently, it has been shown that, upon cooling, disordered Pb(Sc1/2Ta1/2)O3 ceramics transform spontaneously from a relaxor state to a ferroelectric state when processed in a manner that suppresses lead vacancies. If lead vacancies are present, the spontaneous ferroelectric transition is suppressed and the ceramics exhibit the usual relaxor behavior in a wide temperature range. It is shown that disordered Pb(Sc1/2Nb1/2)O3 ceramics have a similar nature: When produced in a manner that does not eliminate lead vacancies, they exhibit normal relaxor behavior. However, if stoichiometry is tightly controlled, disordered Pb(Sc1/2Nb1/2)O3 transforms spontaneously (under zero‐bias field) from a relaxor into a normal ferroelectric upon cooling.

B-Site Order and Infrared Reflectivity in a(B"b"")O3 Complex Perovskite Ceramics

Complex perovskite A(BB)O3 ceramics with various degrees of B-site order have been structurally and spectroscopically characterized by means of x-ray diffraction, transmission electron microscopy, and infrared reflectivity. In Ba(Fe1/2Nb1/2)O3 and Pb(Fe1/2Nb1/2)O3, no order could be detected whereas Pb(In1/2Nb1/2)O3, Pb(Mg1/3Nb2/3)O3, and Pb(Sc1/2Ta1/2)O3 (unannealed) all exhibited weak reflections associated with small ordered regions Pb(SC1/2Ta1/2)O3 was also prepared by appropriate heat treatment in the fully ordered form and exhibited strong maxima arising from the ordered superlattice in both electron and x-rav diffraction. The infrared reflectivity (30-4000 cm-1) revealed correlation between the degree of ordering and appearance of the extra mode in the 260-320 cm-1 range assigned to B-B vibrations. Despite an apparently low volume fraction of ordered material in. partially ordered samples of Pb(SC1/2Ta1/2)O3, the extra mode was observable. It is suggested that infrared spectroscopy is sensitive to short-range ordering down to the nm range which is proposed to exist in between the small regions of order.

Investigation of relaxors that transform spontaneously into ferroelectrics

Abstract B-site disordered Pb(Sc½Ta½)O3 and Pb(Sc½Nb½)O3 can be prepared in a controlled manner to show (a) relaxor behavior and (b) relaxor that undergoes a first order ferroelectric phase transition at zero-bias field. The latter case is a first demonstration of a spontaneous transformation from relaxor to ferroelectric state. TEM, DSC and dielectric and electric characterization techniques are used to investigate this phase transformation and the results are reported. The spontaneous transformation is analyzed in light of existing relaxor models. It is found that cation-anion bond strength can be used as a criterion to predict materials with spontaneous relaxor-ferroelectric transformation.

Comparison of lead zirconate titanate thin films on ruthenium oxide and platinum electrodes

High‐resolution and bright‐ and dark‐field transmission electron microscopy are used to characterize and compare the interface structures and microstructure of PZT/RuO2/SiO2/Si and PZT/Pt/Ti/SiO2/Si ferroelectric thin films, with a view to understanding the improved fatigue characteristics of PZT thin films with RuO2 electrodes. The RuO2/PZT interface consists of a curved pseudoperiodic minimal surface. The interface is chemically sharp with virtually no intermixing of RuO2 and PZT, as evidenced by the atomic resolution images as well as energy dispersive x‐ray analysis. A nanocrystalline pyrochlore phase Pb2ZrTiO7−x, x≠1, was found on the top surface of the PZT layer. The PZT/Pt/Ti/SiO2/Si thin film was well crystallized and showed sharp interfaces throughout. Possible reasons for the improved fatigue characteristics of PZT/RuO2/SiO2/Si thin films are discussed.

Structure of Ba(Y+31/2Ta+51/2)O3 and its dielectric properties in the range 102–1014 Hz, 20–600 K

The goal of this work was to understand the correlation between microscopic material parameters and the dielectric function of candidate materials for applications in the microwave frequency range. The structure and dielectric properties of Ba2+(Y3+1/2Ta5+1/2)O3 (BYT), a typical representative of the Ba(B3+1/2B5+1/2)O3 complex perovskite family, has been investigated from 102 to 1014 Hz and from 20 to 600 K. At Tc=253±1 K, BYT undergoes an equitranslational improper ferroelastic, second‐order phase transition, characterized by the tilting of the oxygen octahedra. The space group symmetry changes from Fm3m, in the high temperature phase, to I4/m below Tc. The existence of an intermediate temperature region (Tc−40<T<Tc) has been observed, where the compound exhibits structural and dielectric properties different from those in the well‐defined high (T≳Tc) and low (T<Tc−40 K) temperature phases. Infrared reflectivity (1012–1014 Hz) and submillimeter transmission (1011–3×1012 Hz) measurements yield dielectric...

Fatigue, rejuvenation and self-restoring in ferroelectric thin films

Abstract The switching, fatigue and rejuvenation phenomena of ferroelectric PZT thin films with differently processed electrode-PZT interfaces and of different thicknesses have been investigated. The ferroelectric contribution to the switching parameters has been isolated from the leakage current contribution, thus allowing the identification of several salient features of the above phenomena. Incorporating our present results with already established properties of PZT thin films, a set of characteristic features of switching, fatigue and rejuvenation is formulated. This set is interpreted using a framework which takes into account the ferroelectric and semiconductor properties of the system. The key issues of the framework are: (i) Strong inhomogeneous built-in electric field exists in virgin films due to contact phenomena. (ii) Extra near-electrode space-charge layers are created during polarization reversal and destroyed by d.c. rejuvenating fields or by the field of fatiguing pulses. (iii) The built-i...

In situ observations of octahedral tilt transitions in strontium bismuth titanate layered perovskites

In situ transmission electron microscopy has been used to study Bi4Ti3O12, SrBi8Ti7O27, SrBi4Ti4O15 and Sr2Bi4Ti5O18, layered perovskites. A cell-doubling phase transition has been found in all compounds at temperatures above the ferroelectric phase transitions. This transition is associated with tilting of the octahedra in antiphase around the c axis, causing doubling in the a,b plane. As the concentration of Sr increases in the compounds the temperatures at which the ferroelectric and cell-doubling transitions occur decrease. However, the rate of decrease for each transition is different and the temperature of the two phase transitions becomes almost coincident in the Sr2Bi4Ti5O18 compound.