| Polycrystalline BaTiO{dollar}sb3{dollar} thin films of approximately 1 {dollar}mu{dollar}m thickness have been synthesized on Ti substrates by an electrochemical process, at temperatures as low as 55{dollar}spcirc{dollar}C. The effect of various processing parameters, such as solution chemistry, atmosphere, quality of substrate surface, applied voltage, current density, temperature and reaction time have been discussed. Formation of BaTiO{dollar}sb3{dollar} is found to be favored only in highly alkaline (pH {dollar}sim{dollar} 14) solutions. Film thickness and uniformity increase with reaction time up to 24 hours. The quantity of total electric charge passed through the electrolytic cell is found to govern the film thickness and uniformity. Use of tetraethylammonium hydroxide, a non-alkali base reagent to adjust solution pH, has resulted in films having improved dielectric properties as opposed to the films prepared with alkali metal bases such as NaOH. Heat treatment at 200{dollar}spcirc{dollar}C further improved the dielectric properties through a phase transition to the thermodynamically stable, ferroelectric tetragonal BaTiO{dollar}sb3{dollar}.; Current work also involves the fabrication and characterization of BaTiO{dollar}sb3{dollar} electrolytic capacitors. Effects of electrochemical processing parameters on the formation of BaTiO{dollar}sb3{dollar} on the surface of sintered porous Ti anode are described. Influence of the purity of Ti powder, porosity of the sintered anode, and post-deposition heat treatment on the dielectric properties of the fabricated capacities are discussed. Complete penetration of the electrolyte solution and an uniform coating of BaTiO{dollar}sb3{dollar} was achieved over the entire surface of Ti using high porosity (35-40% theoretical density) sintered Ti anodes. Samples treated for 8h in 0.5M Ba(OH){dollar}sb2{dollar}-8H{dollar}sb2{dollar}O electrolyte solutions at 100{dollar}spcirc{dollar}C with 12V applied cell voltage showed the formation of dense, uniform BaTiO{dollar}sb3{dollar} coating on the surface of Ti anode. Higher purity (Sumitomo, 99.96% Ti), chloride free Ti powder provided smaller dissipation factors at low frequencies. Heat treatment at 400{dollar}spcirc{dollar}C has significantly increased the capacitance at all frequencies, while it lowered the dissipation factors at low frequencies. Calculated volumetric efficiencies are comparable to those typically obtained for Ta solid electrolytic capacitors. Penetration of colloidal carbon (external) electrode was found to be limited to a depth of 300 {dollar}mu{dollar}m, which might have limited the volumetric efficiencies.; Finally, the electrochemical equilibria in Ba-H{dollar}sb2{dollar}O, Ti-H{dollar}sb2{dollar}O, Ba-Ti-H{dollar}sb2{dollar}O and Ba-Ti-C-H{dollar}sb2{dollar}O systems are represented in the form of E{dollar}rmsb{lcub}h{rcub}{dollar}-PH diagrams. The diagrams are constructed based on the most recent thermochemical data available, at temperatures of 25, 55, and 100{dollar}spcirc{dollar}C. The effect of total activities of dissolved species of Ba, Ti, and C on thermodynamic equilibria has been represented in the diagrams. BaTiO{dollar}sb3{dollar} is found to be the stable phase at high pH and moderate potentials. The presence of even small amounts of carbon, usually in the form of dissolved atmospheric CO{dollar}sb2{dollar}, significantly restricts the stability of BaTiO{dollar}sb3{dollar}. The validity E{dollar}rmsb{lcub}h{rcub}{dollar}-pH equilibrium diagrams obtained for Ba-Ti-H{dollar}sb2{dollar}O and Ba-Ti-H{dollar}sb2{dollar}O systems is verified using the data published in the literature for the hydrothermal and electrochemical synthesis of BaTiO{dollar}sb3{dollar}. |
