Water Vapor Adsorption by Some Manganese Oxide Forms

Abstract

Manganese oxide forms prepared by different methods differ by their compositions, phase ratios in polyphase samples, and crystallite sizes (XRD and TEM characterization). Among the phases, tunnel-structured β-MnO2 (pyrolusite), α-MnO2 (cryptomelane), ε-MnO2 (akhtenskite), and β-Mn2O3 (bixbyite) have been identified. Water vapor sorption isotherms showed substantial differences in the affinities of water molecules to oxide surfaces of the manganese oxide forms under study. The parameters of the BET equation and pore size distribution curves have been calculated. The manganese oxide forms have mesoporous structures characterized by uniform and non-uniform pore sizes as well as by moderate hydrophilic behavior.

Effect of Humidity on the Writing Speed and Domain Wall Dynamics of Ferroelectric Domains

“…It can be seen that at low RH up to ≈ 10%, water adsorbs on BTO surface in non-linear fashion, reaching a plateau of constant water content between 10% and ≈17% of RH. The shape of the adsorption isotherm of water on our BTO surfaces in the measured RH range (Figure 3c), is in good agreement with the trend observed on similar different oxide surfaces [24,[45][46][47] (note that in any case, the final calculation of water thickness in monolayers depends on the structure of the adsorbates layer and also the evolution of the other available species with RH, which can lead to a more pronounced slope for low RH) and is remarkably similar to the shape of the domain width vs RH depicted in Figure 3b, suggesting a link between the two. Each of these curves consists of three regions corresponding to different range of RH: a first region of steep increase in adsorbate thickness/ domain width as a function of humidity, a second region with a plateau, and a third region where adsorbates layer thickness and domain size grow again.…”

“…Quantification of AP-XPS measurements performed on BTO surfaces in controlled RH conditions enabled us to construct the adsorption isotherm for water in the low to intermediate RH ranges. Noting that the size of the written domains as a function of RH and at fixed speed follows the characteristic behavior of water adsorption in different RH conditions, represented by the adsorption isotherm on BTO and other oxides, [24,[45][46][47] we propose that these regimes are consistent with the initial presence of: ice-like highly structured water molecules in regime I, which besides providing low level of dipolar screening also prevent redistribution of surface charges by hopping, necessary in attending the screening demands (and therefore screening becomes slow in a nominally insulating ferroelectric film); ice-like and incomplete liquid-like water coexisting in regime II, with a higher dielectric constant and therefore higher capacity for dipolar screening but still limited ionic mobility, and a complete layer of liquid water on the surface of the film in regime III, which provides efficient screening via fast ionic mobility along the surface.…”

Manganese oxides synthesized via microwave-assisted hydrothermal method: phase evolution and structure refinement

“…The thermal analysis up to 1200 ºC (thermogravimetry and differential scanning calorimetry) of the MnO sample is shown in Figure 2. Two endothermic reactions are observed up to approximately 117 ºC, accompanied by a weight loss of 1.34%, which are associated with the dessorption of molecules on the sample surface, usually water molecules, a common phenomenon that occurs in this type of oxide [44].…”

Manganese oxides synthesized via microwave-assisted hydrothermal method: phase evolution and structure refinement

“…2. Two endothermic reactions are observed up to approximately 117 ºC, accompanied by a weight loss of 1.34%, which are associated with the dessorption of molecules on the sample surface, usually water molecules, a common phenomenon that occurs in this type of oxide [42].…”