The growth mechanism is governed by a competition between the arrival rate of Pb and their re-evaporation from the film during the growth. The in situ formation temperature of the perovskite phase increased when the incident Pb flux increased. As a result, PbTiO3 films have been prepared at low temperature with appropriate combination of the substrate temperature and the lead content in the target, i.e., the sputtered lead flux. Since the lead sticking coefficient is very sensitive to the substrate material, the perovskite phase appears at different temperatures, depending on the substrate nature. PbTiO3 films are obtained at 550 °C on Al2O3 and SrTiO3 substrates; on Si/SiO2/Ti/Pt substrates, stoichiometric films are obtained at 440 °C. The structure and the microstructure of the films were examined at various deposition conditions. The substrate temperature strongly influenced the film orientation, and the crystallinity depended on the incident lead flux. High quality thin films (FWHM = 0.2°) are obtained at 550 °C on SrTiO3 substrates. The films deposited at 440 °C on Si/SiO2/Ti/Pt show ferroelectric properties. This self-controlling mechanism of the stoichiometric composition allows the growth of ferroelectric films at low temperature, compatible with semi-conductor technologies for the realization of integrated circuits.

A new generation of target has been identified to deposit lead based perovskite films through the RF magnetron sputtering method. PbTiO3 and Pb(Zr,Ti)O3 thin films were sputtered from (PbO,TiO2) and (PbO,TiO2,ZrO2) targets. The film composition was controlled by simply modifying the thickness of each oxide layer. The sputtered area of each oxide is also well-defined and allows to achieve reliable compositions of the film deposited. Relations were established between the compositions of the target and the films. The evaluation of each oxide area could also be calculated corresponding to any desired film composition whatever the element. Better distribution of the doping agent was also achieved with this multilayer target.

Three alumina/3 mol % Y2O3 doped zirconia mixed powders were synthesised using a hydrothermal route. They contained respectively 5, 25 and 50 volume% of zirconia. Pressureless sintering of the 5 volume% composition and uniaxial hot pressing of the 5 and 50 volume% compositions were studied. The as obtained nanocomposites were characterised microstructurally and mechanically for the 5 and 50 vol% composites. An improvement of toughness was observed for these two nanocomposites and is discussed as a function of observed microstructure and rupture faces. Finally, an approach of superplasticity was developed in a thermo-compression test of a 5, 25 and 50 volume% ZrO2 composites layered packing system.

The interconnections in a porous biomaterial are the pathways between the pores. They conduct cells and vessels between pores. Thus they favour bone ingrowth inside ceramics. The aim of our study was to determine the effect on bone ingrowth of interconnections in two ceramics: hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) with the same porosity of about 50% and a mean pores size of 100–300 μm and a mean interconnection size of 30–100 μm. In vitro, four discs for osteoblast culture were studied after 14 and 28 days of incubation. The results show that human osteoblasts can penetrate interconnections over 20 μm in size, and colonize and proliferate inside macropores, but the most favourable size is over 40 μm. In vivo, eight cylinders were implanted in the middle shaft of both rabbit femurs for 12 or 24 weeks. The histomorphometric results show that interconnections in porous ceramics favour bone ingrowth inside the macropores. In the HA group the rate of calcification and bone ingrowth do not differ, and chondroid tissue is observed inside pores. But in β-TCP, the calcification rate and the bone ingrowth increased significantly. At week 12 significant correlation between new bone ingrowth and the size of the interconnections is observed between new bone ingrowth and the density of pores. In conclusion we notice that in vivo a 20 μm interconnection size only allows cell penetration and chondroid tissue formation; however the size of the interconnections must be over 50 μm to favour new bone ingrowth inside the pores. We propose the concept of “interconnection density” which expresses the quantity of links between pores of porous materials. It assures cell proliferation and differentiation with blood circulation and extracellular liquid exchange. In resorbable materials, pore density and interconnection density are more important than their size, contrary to unresorbable materials in which the sizes and the densities are equally important. © 1999 Kluwer Academic Publishers

The combined influences of KOH initial concentration and initial lead precursor excess on the characteristics (morphology, powder density, specific surface area, crystalline structure and powder chemical composition) and sintering behaviour of hydrothermally synthesised powders, have been investigated. Optimised conditions (low KOH concentration and presence of lead excess in the feedstock) have been determined that lead to fine deagglomerated and reactive PZT powders densifying at about 850°C. A Pb-rich surface layer has been identified over the grains, that is responsible for this low sintering temperature. Despite the large excess of lead, the core of powders remains lead deficient. But by lowering [KOH]o, it is possible to keep the lead deficiency within a few percent.

Thin films of lead titanate (PbTiO3) were prepared on silicon substrates by sputtering. Two processes have been developed; (a) the in situ process (the growth temperature was 440 °C) and (b) the deposition at room temperature followed by a conventional annealing at 680 °C. The dielectric constant, the ferroelectric, and the piezoelectric properties were evaluated and compared. The dielectric constant of films deposited in situ was higher than those of postannealed films likely due to the dense microstructure with fine and homogeneous grains. The embedded beam method and the Berlincourt piezometer were used to measure the e31 and the d33 piezoelectric coefficients, respectively. The PbTiO3 films were naturally polarized, in particular the films grown in situ have large piezoelectric constants: e31=−0.49 C/m2 and d33=20 pC/N. These values agree broadly with data of bulk ceramics, however, with bulk material a poling treatment is necessary to attain these values. The poling of the postannealed films leads to a substantial increase of their piezoelectric properties; e31=−0.26 C/m2 and d33=8 pC/N for virgin film and e31=−0.41 C/m2−d33=18 pC/N for an applied electric field of 110 kV/cm (close to saturation) and a poling time of 30 min. The piezoelectric response was found to depend on the direction of the poling field. Note d33 and e31 decreased when the poling field was applied against the preferred polarization direction; the polar domains were oriented from the film surface to the substrate.

In order to understand the influence of the implantation site on bone biomaterial evaluation, we implanted cylinders of HA and beta-TCP ceramics in the femoral diaphysis and condyle of rabbits. After 3, 8, 12, and 24 weeks of implantation, histological investigation and histomorphometry were performed on undecalcified samples. Our results show that spontaneous bone healing in the empty cavities is significantly different (p < 0.05) between cortical (SBH > 80%) and cancellous bone sites (SBH < 31%) and that no new bone is formed in marrow tissue. For both porous ceramics, the highest osteogenesis was obtained in the cortical site. Osteogenesis was intermediate in the cancellous site and weak in the medullar site. The material biodegradation was the strongest in the medullar site and higher in the cancellous site than in the cortical site. Both activities were better in the beta-TCP than in the HA (p > 0.05). The marrow tissue presents a foreign-body reaction more reliable, sensitive, and durable than other bone tissues. Therefore, the cancellous bone site is a good site for evaluation of the biofunctionality of biomaterials because of the equilibrium of the osteogenesis and the biodegradation activities, but marrow tissue seems to be better for testing material biocompatibility in vivo.

A new process, based on the simultaneous gelling of alumina/zirconia precursors followed by hydrothermal treatment, may be used to produce mixed oxides composite powders with increased homogeneity. The aim of this paper is to present zirconia powders characteristics as a function of synthesis conditions. Crystallite sizes are determined by X-ray diffraction, specific surface area by B.E.T. method, density by helium pyenometry. Powders are observed by T.E.M..

The orientation of Pb(Zr,Ti)O3 (PZT) thin films grown by sputtering on a Si/SiO2/Ti/Pt substrate using a PbTiO3 (PT) buffer layer was controlled by changing the thickness of the buffer layer. The x-ray diffraction of PT as a function of the thickness, in the range of 20–400 Å, showed modification of the PT orientation. That suggests a gradual evolution of the lattice parameters in the nucleation stage of PT films. The main growth mechanism was certainly due to the passing from an island growth to a continuous layer. The (111) oriented and (100) oriented PZT films were grown on 50 and 200 Å PT buffer layers, respectively.

PbTiO3 (PT) based ferroelectric capacitors have been produced in-situ on GaAs substrates by r.f. magnetron sputtering. Stoichiometric films have been obtained in the temperature range 440 degrees C - 460 degrees C without any substrate degradations. X-Ray diffraction results show that pure perovskite structure is obtained in-situ without post-annealing treatment. The PT film is polycrystalline without any preferred orientation. Electrical properties of the films have been evaluated, in particular the ferroelectric properties have been tested.

Lead titanate thin films have been formed on Si(100)/SiO2/Ti/Pt substrates by sputtering followed by a post-deposition annealing. Pure perovskite phase is obtained at a temperature compatible with silicon technology; the films are dense without porosity. The ferroelectric and piezoelectric properties of the films have been determined. The embedded beam method is used to measure the piezoelectric response. The effect of poling on the piezoelectric properties is evaluated. The results show that this thin-film material has promise for use in actuation, in particular, to integrate PbTiO3 films into ambitious silicon micromachining schemes.

The growth of piezoelectric and ferroelectric thin films is presented in this paper. The materials studied are : PbTiO3, PbLaTiO3, PbZrTiO3 and LiNbO3. These materials presents excellent piezoelectric properties and will must have an important impact in the microsystem (micro-sensors, micro-moving) and micro-optoelectronic development (integrated optics). In thiscontext, a monolithic integration will be a desicive parameter but with this strategy it is necessary to find a technological compatibility between semiconductor materials (silicon, gallium arsenide) and these materials (growth or annealing temperature, etching...). The films are deposited by R.F. magnetron sputtering ; we have used different substrates but we present only here the results obtained on silicon substrates. Two processes have been developed: The growth is made at room temperature and a post-annealing treatment is necessary tocrystallize the film. Two annealing treatments have been optimized: Conventionalannealing and rapid annealing. The growth is made with substrate heating ; the main objective is to obtain the desired structure without annealing treatment. The growth conditions and the annealing processes are presented ; the electrical properties of the filmsare also evaluated.

Thin films of lead titanate were prepared in-situ using radiofrequency magnetron sputter-deposition. The in-situ perovskite phase formation has been studied as a function of the substrate material, the substrate temperature (T-S) and the sputtered lead flux. The incident lead flux is controlled by the lead content in the target (X). Perovskite phase can be obtained under a relatively wide range of sputtering conditions with control of the Pb content in the film. The formation temperature of the perovskite phase increased when the incident Pb flux increased. With an appropriate combination of T-S and X, it is possible to grow, at relatively low temperature, stoichiometric thin films compatible with semi-conductor substrates. For example, PbTiO3 films have been deposited on silicon and gallium arsenide substrates at 440 degrees C; these films present ferroelectric properties.

Our study would find the role of porous interconnections (PIC) on bone ingrowth and material degradation in tricalcium phosphate beta (P-TCP) with about 50% porosity, a size of 100-300 mu m macropores and of 30-100 mu m PIC. In vitro, human osteoblasts were cultivated on discs with two delays: 14 and 28 days. In vivo, implants were implanted in middle diaphysis of both femurs with two delays: 12 and 24 weeks. The in vitro and in vivo samples were observed with histomorphometry (HMM) and scanning electronic microscopy (SEM). In vitro results show that human osteoblasts penetrate sizes of PIC over 20 mu m diameter (dia.), set up and grow inside the bioceramic macropores. In vivo HMM results shaw that PIC directly influence bone ingrowth inside pores and material degradation. We notice that a PIC size over 50 mu m dia. allows formation of new bone ingrowth inside the pores. The PIC density expresses the link between pores inside porous materials, assures the cells proliferation and tissular differentiation by extra cellular and vascular exchanges. In resorbable materials, pores and PIC initial densities play a more important role than their sizes.

Lead-based ferroelectric thin films, PT and PZT, have been deposited on platinized silicon substrates by using rf magnetron sputtering technique. Whatever the deposition network, the piezoelectric character has been demonstrated for all films. The piezoelectric response dependence of the poling treatment with the time and the applied de electric field has been studied. The in-situ deposited films, without previous poling, present piezoelectric activity e(31PT) = -0.49 C/m(2). The post-annealed films have a slight piezoelectric activity without poling treatment and maximum values of the piezoelectric coefficients have been obtained, e(31PT) = 0.41 C/m(2) and e(31PZT) = 3.84 C/m(2) with de electric field of 100 and 150 kV/cm respectively. The piezoelectric responses are directly related to the structure of the films, they are discussed in terms of domain orientation during the films formation and during the poling treatment.

The influence of growth conditions and post-annealing treatments on radio frequency (r.f.) magnetron sputtered lead zirconate titanate (PZT) thin films have been investigated. By adjusting the plasma discharge parameters, it is possible to control, with stoichiometric single oxide target, the film composition precisely. No excess lead was used either during sputtering (in the target) or during post-deposition annealing. The structural, microstructural and electrical properties have been systematically examined as a function of the annealing treatments. Perovskite structure was obtained by conventional annealing as well as by rapid thermal annealing. The films were dense and crack-free; the film orientation, the microstructure and the surface morphology are directly related to the thermal processes. The ferroelectric properties in terms of coercive field and remanent polarization are also very sensitive to the annealing treatments. (C) 1997 Elsevier Science Limited.

Dual Energy X-ray Absorptiometry (DXA) allows direct measurement of bone mineral content. We evaluated its interest for evaluation of porous ceramics before and after bone implantation. HA and beta-TCP implants were inserted in 3 mm diameter cavity of rabbit femur with 3 delays (T0, T12 and T24 weeks) for DXA and histomorphometric analysis. Om results show excellent new bone contact in interface implant/bone for the two ceramics. Bone ingrowth and biodegradation were more important in beta-TCP than in HA. Comparison of the sites, bone ingrowth activity was cortical > cancellous > marrow site. But biodegradation activity was marrow > cancellous > cortical site. After comparison of the two methods, we consider that DXA can bring complementary inquiries in the evaluation of porous ceramics. Its non invasive and atraumatic character should permit in vivo longitudinal survey, and analysis of biodegradation in resorbable ceramics and bone rehabitation in non resorbable ceramics.

Nous presentons dans cet article nos principaux resultats obtenus sur la croissance de films minces piezoelectriques et ferroelectriques. Les materiaux etudies sont : PbTiO 3 - PbLaTiO 3 - PbZrTiO 3 et LiNbO 3 . Ces materiaux presentent d'excellentes proprietes piezoelectriques et devraient avoir un role fondamental dans le developpement des micro-systemes (micro-capteurs, micro-deplacements, ...) mais egalement de la micro-opto-electronique (optique integree). Dans ce contexte, une perspective d'integration monolithique serait un atout majeur ce qui impose une compatibilite technologique entre les materiaux semiconducteurs (silicium, arseniure de gallium) et ces materiaux (temperature de croissance ou de recuit, gravure, ...). Les films sont deposes par pulverisation cathodique R.F. magnetron ; nous avons utilise differents types de substrats mais nous nous limitons, dans cette presentation, aux resultats obtenus sur des substrats de silicium. Deux filieres de depot ont ete mises au point : - Les depots sont realises a froid et un recuit post-depot est necessaire pour cristalliser le films. Deux voies de recuit ont ete developpees : le recuit conventionnel et le recuit rapide. - Les depots sont realises en temperature , l'objectif est d'atteindre la structure souhaitee sans recuit post-depot. Les conditions de depot et de recuit sont presentes et les proprietes electriques des films evaluees.