Novel tungsten oxides and molybdenum oxides: Low-temperature syntheses, characterizations and their applications in the energy area

Novel tungstates with pyrochlore structure have been synthesized using mild hydrothermal methods in the presence of small cations such as Na{dollar}sp+{dollar} and NH{dollar}sb4sp+{dollar}. The products are pH as well as temperature dependent. AC impedance conductivity measurements revealed that the ions in the pyrochlore structure show rapid mobility. The room temperature conductivity of hydronium pyrochlore reaches 7 {dollar}times{dollar} 10{dollar}sp{lcub}-4{rcub}{dollar} S/cm, close to that of the best protonic conductors and it exhibits a strong dependence on the water partial pressure, which should permit it to be used as a humidity sensor. The chemical diffusion coefficient of the Li{dollar}sp+{dollar} ion D{dollar}sb{lcub}rm Li{rcub}{dollar} in a hydrothermally deposited pyrochlore film was determined to be 1.1 {dollar}times{dollar} 10{dollar}sp{lcub}-7{rcub}{dollar} cm{dollar}sp2{dollar}/s, which is among the highest values reported for WO{dollar}sb3{dollar} films and makes it of great interest for use in practical electrochromic devices and windows. The structural aspects, ion-exchange and intercalation reactions of these pyrochlores were also investigated.; When we systematically varied the templating ions from NH{dollar}sb4sp+{dollar} through {dollar}rm Nsp+(CHsb3)sb{lcub}n{rcub}Hsb{lcub}4-n{rcub} (for 1 leq n leq 4) to (CHsb3CHsb2)sb4Nsp+{dollar}, pyrochlore tungstates and Keggin-like clusters were formed. Using the tetramethyl ammonium ion (TMA) we obtained single crystals of {dollar}rmlbrack N(CHsb3)sb4rbracksb6Hsb2Wsb{lcub}12{rcub}Osb{lcub}40{rcub}{lcub}cdot{rcub}2Hsb2O{dollar} which were large enough to allow crystal structure determination. The crystals are orthorhombic, space group Pnma (No. 62), a = 21.90(1), b = 21.507(7), c = 13.27(1) A, Z = 4. The structure contains an almost close-packed array of Keggin ions, {dollar}rm Hsb2Wsb{lcub}12{rcub}Osb{lcub}40{rcub}sp{lcub}6-{rcub}{dollar}, between which reside the NMe{dollar}sb4sp+{dollar} ions. A silver tungstate with hexagonal tungsten bronze was synthesized for the first time by the hydrothermal approach when Ag{dollar}sp+{dollar} was used as a template ion.; The hydrothermal technique was extended to the molybdenum oxides. Reaction of acidified M{dollar}sb2{dollar}MoO{dollar}sb4{dollar} solutions at 150{dollar}spcirc{dollar}C for three days led to a range of structures depending on the metal M. Hexagonal molybdates with the general formula {dollar}rm (Msb{lcub}y{rcub}{lcub}cdot{rcub}zHsb2O)Mosb{lcub}6-x{rcub}Osb{lcub}18-x{rcub}Hsb{lcub}4x-y{rcub}{dollar} are formed when M is a small cation such as Na{dollar}sp+{dollar}, NH{dollar}sb4sp+{dollar} and Ag{dollar}sp+{dollar}. These molybdates crystallize as hexagonal rods and have the space group P6{dollar}sb3{dollar}/m. The open structure of these hexagonal molybdates allows the M ions in the tunnels to be readily mobile and permits the ready intercalation of additional cations such as hydrogen and lithium. Upon continuous ion exchange of sodium molybdate with 6N HNO{dollar}sb3{dollar}, a new hydrate {dollar}rm MoOsb3{lcub}cdot{rcub}0.6Hsb2O{dollar} was formed. Subsequent dehydration of this hydrate results in the formation of a new hexagonal modification of "MoO{dollar}sb3{dollar}". The structural features, thermal properties, diffusion and reactivity of these phases have been determined. The use of these hexagonal molybdates in lithium batteries was tested and initial positive results were obtained.; The use of the TMA template in the hydrothermal synthesis of molybdenum oxides leads to a novel compound with a layered structure built of from Mo{dollar}sb4{dollar}O{dollar}sb{lcub}12{rcub}{dollar} building blocks. It has the formula {dollar}rm (NMesb4)Mosb{lcub}4-delta{rcub}Osb{lcub}12{rcub} (deltaleq 0.2){dollar} and crystallizes in the monoclinic system with a = 11.331, b = 11.949, c = 11.140 A and {dollar}beta{dollar} = 108.1{d...