tailieunhanh - Ferroelectrics Physical Effects Part 16

Tham khảo tài liệu 'ferroelectrics physical effects part 16', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 590 Ferroelectrics - Physical Effects interdiffusion and chemical reaction between the film and the substrate is suppressed. For example Ohba et al. 1994 observed a steep gradient of chemical composition between a substrate and a PZT layer an interfacial Ti-rich PZT layer with low piezoelectric constant near the substrate. Contrary to this result Morita et al. 1997 reported that separated PTO and PZO layers were deposited during the nucleation process the PTO layer grew during the first 2 h of the nucleation process followed by the PZO film growth Fig. 7 Case 3 . Gradient in sol-gel PZT thin films A great number of sol-gel processing paramiters as temperature pyrolysis and final heattreatment heat treatment atmosphere and duration solution composition and seeding layer are strongly influencing the structural and therefore physical properties of PZT films. Broad studies have been done on chemical depth profile of sol-gel PZT films depending on the process conditions mention above. Some examples of chemical depth profile for sol-gel PZT films on platinized Si regarding solvents pyrolysis and annealing are given in . As can be seen it is not evident whether initial sol or annealing is responsible for the gradient appearance. One of the major limitations of the sol-gel technique is that it does not yield the desired perovskite phase directly. Thermodynamically driven diffusion and or kinetic demixing for sol-gel films are strongly determine by how the annealing is accomplished furnace hot plate rapid thermal annealing temperature duration etc lead content of the starting solution and also thermal decomposition of raw components. Quite often some of these factors are not mentioned in the publications and it makes difficult or even impossible to do comparisons and reasonable conclusions of these studies. The formation of perovskite phase upon final annealing is preceded by an undesirable nonferroelectric pyrochlore phase. Pyrochlore inclusions are often observed