Preparation And Characterization Of Functional Materials (d) Kdp Crystal Of Bto Thin Film And Nanocrystalline Study

Potassium dihydrogen phosphate (KDP) and its deuterated analog KD₂PO₄ are a type of excellent electrooptical non-linear optical materials. KDP-family crystals are widely applied in the field such as laser radiation electro-optical modulation, light deflectors and optical rapid switches. Recently, with the development of program of inertial confined fusion (ICF), the higher standard of KDP-type crystals in rapid growth and optical properties is proposed, which contains larger scale in size, higher optical laser damage threshold, lower absorption and higher homogeneity.Aiming at the main the disadvantage of the four-chamber circulation method, we designed two-vessel-four-zone-crystallizer system, which consist of the merits of the circulation method and the ones of simpler units for easier operation. And the parameters for rapid growth excellent crystals were determined through theoretical analysis and experimental methods. High quality crystals can be obtained using the system, which confirmed by the investigations of X-ray diffraction (XRD), deuterium content, uv-vis-nir transmission spectra, trace metal impurities concentration, electro-optical and thermal properties.The space group theoretical analyses and assignment of the lattice vibration modes of the KDP and DKDP crystal with various geometries have been performed. The lattice vibration spectra of KDP, which arise mainly from internal vibrations of the H₂PO₄^- anion. are studied by Raman scattering measurements. The results are consistent with the space group analyses. The H₂PO₄^- cluster is mainly ascribed to four vibrations, as an asymmetrical P(OH)₂ stretching vibration (v₁), an in-plane P(OH)₂ bending vibration (v₂). a PO₂ bending vibration (v₃), and an in-plane PO₂ symmetrical stretching vibration (v₄). The four characteristic vibrational modes appeared at 917, 364, 1035, and 523 cm^-1 in KDP. are red shift to 883, 361, 998, and 516 cm^-1 in DKDP, respectively. The red shift is more remarkable for O-H vibrational mode caused by the so called isotope effect, which gives the explain for the wider transmission zone in KDP than that in DKDP.The structural parameters and electronic structure were calculated by first principles. We found that the geometric isotopic effect was not able to completely explain the largedifference in the Curie temperature Tc between KDP and DKDP. It should combine the proton tunneling quantum effect, proton-lattice coupling or the coupling displacive and order-disorder models to describe the huge isotopic effect upon deuteration.The electronic structure calculation shows the significant orbital hybridization between D/H. P, and O atoms. The interaction is covalent among the three atoms, and ionic between K and PO4. The wider forbidden band gap causes the higher laser induced damage threshold of KDP, comparing to DKDP.From results of AFM, the formation mechanism of defect can be seen clearly, when the impurities inhibited, were absorbed onto the surface. The advancing of step would be macro-steps formed, then caused the defects. The higher super-saturation aggravated detect in KDP crystals for higher super-saturation improved the effect of impurities. The existence of growth dislocation, growth bands, growth striation will also form the inclusions of solution, causing defect.As an important ferroelectric material with perovskite layer structures, bismuth titanate (Bi4Ti3Oi2(BTO)) has a low dielectric permittivity, high Curie temperature, and large spontaneous polarization, consequently it has wide application, such as nonvolatile memory devices and ferroelectric field effect transistor (FET) memory devices of nondestructive readout modes. BTO ceramics have been used in capacitors, transducers, sensors, etc. The tuning of electric properties by compositional modification as well as the size effect can meet commercial specifications for Curie temperature, conductivity, coercivity. compliance, etc. Among the various techniques available for the fabrication of BTO nanomaterials, metalorganic decomposition (MOD) method employed in this study offers the advantages of simplifying process, better homogeneity, stoichiometric composition control, and low cost. In view of these, the BTO series thin films and nanocrystals and ceramics have been prepared using MOD technique, and their special properties were analyzed.Homogeneous and fine BTO and ceramic powders with the average sizes of grains around 100 nm have been prepared by MOD method. The synthesis temperatures (-900° C) employed are substantially lower than those currently used in the conventional route (-1100° C). Dielectric investigations in bulk ceramics show that La concentration in BLTXceramics have a great influence on the dielectric permittivity, dielectric loss and Curie temperature, which mean that La can be used to tune the electric properties of BTO ceramics to meet the commercial requests of Curie temperature, conductivity, coercivity, compliance, etc.The dielectric constant of the BSmTo.ss capacitor slightly decreased with increasing frequency. Room temperature resistivity of 108 -10" Q cm and leakage current of less than 10"8 A were obtained for the film, establishing good insulating behavior. The I-V characteristics revealed ohmic conductivity in the lower voltage range and space-charge-limited conductivity at higher field. The counterclockwise hysteresis inferred that the ferroelectric property sufficiently controlled the silicon potential. The shift of some modes to higher wavenumber implied an increase in structural distortion due to the changed ionic radius and atomic mass of Sm ions. To sum up, the appropriate Sm-content substituted BSmT thin films, x=0.5 for example, displayed preferably electrical and memory properties which had promising applications as FFET memories.Space group theoretical analysis was applied to calculate the maximum vibration modes in a BTO primitive cell. Raman scattering and infrared absorption measurements of BTO nanocystals showed a large decrease of the number of peaks, which could be interpreted by the fact that the characteristic vibrational modes of BTO nanocrystals arise mainly from the internal modes of TiO6 octahedra. Experimentally, modes counting in the Raman spectra of BTO is never quite exact because of possibility of overlapping bands, bands formally allowed but too weak to observe, and bands that maybe multi-phonon features. The TiO6 octahedra showed considerable distortion at room temperature so that some phonon modes appeared wide and weak. The amendment of ferroelectricity is therefore expected due to the variation of electronic structure in nature with ion modification of Bi. Raman shifts and infrared absorption bands in BTO nanocystals were tentatively assigned referring the vibrational modes of metal-oxygen anion groups, which is helpful for the study on the formation mechanism of BTO series nanomaterials.The reaction mechanism of BTO nanocrystals and ferroelectric thin films were investigated with XRD, DT/TGA, IR and Raman experiments, which can be summarized as follows, a) Minor BTO emerged in the precursor after 90° C heating, and nitratedecompose with the increasing temperature, b) The bismuth carbonate might appear with the increase temperature, and it will decompose at higher temperatures. The synthesis of the BTO compound takes place through the formation of an intermediate phase of composition Bii2TiO20- Prolonged heat treatment promote a rapid consumption by solid-state reaction of the intermediate phase with the formation of BTO, without any indication on the formation of other different phases or segregation of the individual metal oxides, c) The lattice-match effect might be the reason for the different reaction route between the BTO thin films and nanopowders formation. The Perovskite is the sole phase during the BTO crystallization, d) BTO was formated at temperature of 600° C, and better crystallinity and an increase in grain size with the increase annealing temperature.