Synthesis of Mixed Conducting Oxides by An Organic Steric Entrapment Method

Comparative study of titanate syntheses by the organic steric entrapment method

“…However, the process is often expensive and complicated. The organic steric entrapment method using polyvinyl alcohol (PVA), polyethylene glycol (PEG), or ethylene glycol (EG) as a polymer carrier has been developed to facilitate and make the soft solution processing more efficient 2–35 . The PVA, partially substituted with 17 mol% acetate groups, ensures a homogeneous distribution of the metal ions in its polymeric network structure and inhibits their segregation and/or precipitation from the solution.…”

“…It is hypothesized that the small size of the titania particles will allow a homogeneous reaction of the titania with the metal cations sterically entrapped in the PVA polymer. 3,16,18 Generally, the PVA and EG methods have a distinct advantage over other sol-gel methods in that they are easier, more efficient, cheaper, and allow homogeneous mixing of cations in solution, rather than in the solid under prolonged high temperature, solid-state diffusion. of two-component titanate powders, the nitrate solutions were first added to the EG and heated to 80 • C, while mixing, until they were fully dissolved.…”

“…This serves to decrease the mobility of metal ions and constrain the system to prevent precipitation of cationic species and agglomeration. The organic–inorganic powder synthesis method involves mechanical, steric entrapment, but also some chemical chelation, as is schematically depicted in Figure 1 for an example of CaAl 2 O 4 synthesized by the PVA method 2–36 . At the optimum amount of polymer, the metal ions are dispersed in solution and a homogeneous, polymeric network is formed which prevents them from precipitating.…”

“…For the three‐component system (PZT), an alternative water‐soluble PVA system was utilized in conjunction with a stable, nanosized titania sol. It is hypothesized that the small size of the titania particles will allow a homogeneous reaction of the titania with the metal cations sterically entrapped in the PVA polymer 3,16,18 . Generally, the PVA and EG methods have a distinct advantage over other sol‐gel methods in that they are easier, more efficient, cheaper, and allow homogeneous mixing of cations in solution, rather than in the solid under prolonged high temperature, solid‐state diffusion.…”

“…However, by using in situ EG polymerization around the Ti 4+ species, this process can be extended to chemicals that decompose in water and precipitate out of solution, such as titanium isopropoxide Ti[(OCH(CH 3 ) 2 ] 4 or “TISO.” 3 In the case of titanate powder, EG can act as an effective solvent for wet chemical synthesis, because a water‐soluble titanium salt is not available commercially. The polymerizing agent, EG in this method, acts to capture the metal ions by polymerizing around the dissolved Ti 4+ species resulting in a steric entrapment mechanism as in the PVA method 2–35 . This serves to decrease the mobility of metal ions and constrain the system to prevent precipitation of cationic species and agglomeration.…”