The Studies On The Preparation And Properties Of Lanthanum And Calcium Modified Lead Titanate Ferroelctric Thin Films

In this thesis, the two kinds of ferroelectric thin films with perovskite structure were prepared by three important process techniques. The PLCT, PT/PLCT/PT ferroelectric thin films were prepared on Si and Pt/Ti/SiO₂/Si substrates by the sol-gel technique; the PLCT thick film were prepared on Si and Pt/Ti/SiO₂/Si substrates by the modified sol-gel techniques; the PLCT ferroelectric thin film were prepared on Si and Pt/Ti/SiO₂/Si substrates by radio-frequency magnetron sputtering with PLCT ceramic targets.The following research works have been done: the preparation of the PLCT sol, the PLCT nanometer powders, PLCT thin films, PT/PLCT/PT heterostructure thin films and PLCT thick film by sol-gel techniques, the preparation of the PLCT thin film by RF-magnetron sputtering. The crystalline properties of the nanometer powders of PLCT have been studied by means of modern analyses techniques such as XRD, laser scattering grain analyses instrument, RAMAN spectroscopy. The crystalline properties, chemical composition, chemical state of various elements, surface morphology, and domain structure of films have been studied by means of modern analyses techniques such as XRD, XPS, EDAX, SEM, AFM, PFM, SNDM, etc. The electronic properties of PLCT series multilayered ferroelectric hetero-structures thin films were measured. The main conclusions with innovation significance are as follows:1. It has been studied that the relation between the stability of perovskite structure and the radii of positive ion, composition and stability of electrovalent bond, electrical structure of positive and negative ion, et.al. The stable factor of perovskite structure was calculated. It was concluded that the more percent Ca into the PLT, the higher the formation factor F of PLCT, the perovskite structure of PLCT is more stable and the perovskite structure of PLCT could be formed at lower annealedtemperature.2. The optimized techniques of utilizing sol-gel technology for preparing PLCT ferroelectric thin films, PT/PLCT/PT ferroelectric heterostructure thin films and PLCT ferroelectric thick films were attained through a large of experiments' studies and the analyses of properties of the ferroelectric thin films. The PLCT ferroelectric thick films with pure perovskite structure were fabricated by a modified sol-gel process..3. Nanometer PLCTx powders were prepared by the sol-gel technique. The soft modes of PLCTx nanometer powders were investigated by using Raman scattering. Raman spectrum analysis shows that the frequencies of some modes decrease and some of modes disappear. It was caused by the Ca ion and La ion replaced the Pb ion of A position in perovskite compound, that bring lattice mismatch and asymmetrical replace. The low frequency phonon mode of PLCT (lOOx) Raman spectrum is attributed to the deviation of Ca2+ and La3+ in A location of the perovskite structure; and high frequency phonon mode is attributed to the deformation of TiC>6 octahedron, which is resulted by the deviation of the atoms in TiC>6 octahedron from ideal position4. The composition and binding energy of PT/PLCT/PT heterostructure films and PLCT thick films were investigated by XPS. The Pb element of PT/PLCT/PT heterostructure thin film exist as PbTiO3 compound on the surface, there is also a little Pb element on the surface; on the other hand, the Pb element exist as Pb single substance and PbTiC>3 compound in the inner of the thin films. The Pb element of PLCT thick film exist as PbTiC>3 compound on the surface, on the other hand, the Pb element exist as Pb single substance and PbTiO3 compound in the inner of the thick films. Compared with the binding energies before the erosion, it was found that the binding energies of every elements of PT/PLCT/PT thin films and PLCT thick films after erosion 3000 A by Ar+ increase in different degree. It was regard that the Pb single substrate of thePT/PLCT/PT thin films and PLCT thick film mainly due to the Pb overplus, Pb volatilization, and Ar+ sputtering during the erosion.5. The surface morphology of PLCT ferroelectric thin films was studies by AFM combined with other analysis techniques (for example SEM). It shows that the surface of PLCT thin films is rather smooth and continuous. The ED AX analysis of PLCT thin films shows that the atomic ratio of PLCT thin films is closed the ideal chemical mole ratio of PLCT thin films.6. The domain properties of PLCT ferroelectric thin films were firstly studied by PFM and SNDM. The domain sizes of PLCT ferroelectric thin films gradually increasing with the annealed time increasing. It was found that the domains of PLCTthin films was mainly existed as 180° domain formation. The formation of the in-of-plan domains and the out-of-plan domains on the surface of PLCT thin films is different each other. The results of SNDM analysis summarized synthetically the distributing properties of the in-of-plan domain and the out-of-plan domain on the surface of the PLCT ferroelectric thin film.7. The electrics properties of PLCT series ferroelectric films were measured. It was concluded that the dielectric constants of PLCT series ferroelectric films decrease following with the frequency increasing, the dielectric loss of PLCT series ferroelectric films firstly decreased and then increased following the frequency increasing; the resistivity of PLCT series ferroelectric films decreased following with the frequency increasing. The typical value of pyroelectric constants of PLCT ferroelectric thin films and thick films are 1.6 -2.1 X 10"8C/cm2K.