过渡金属离子掺杂纳米TiO2的相变与光催化活性

采用溶胶-凝胶法制备了掺杂Mo⁶⁺、Cr³⁺、Fe³⁺的改性纳米TiO₂光催化剂，并分别在550℃和580℃下对其进行了热处理，考察了热处理温度对掺杂纳米TiO₂相变和光催化活性的影响.通过光催化降解染料罗丹明B实验，对在不同热处理温度下Mo⁶⁺、Cr³⁺、Fe³⁺改性以及不同Mo⁶⁺掺杂量的TiO₂光催化活性进行了评价，发现掺杂离子对TiO₂光催化活性的影响与其对TiO₂相转变的作用是一致的，即抑制相转变的同时也提高了光催化活性.实验结果也进一步表明，Mo⁶⁺掺杂量为0.05％（摩尔分数）时的TiO₂具有最佳光催化活性.     

Removal of phosphate ions with a chemically modified chitosan/metal‐ion complex

The adsorption of metal ions (Mo⁶⁺, Cu²⁺, Fe²⁺, and Fe³⁺) was examined on chemically modified chitosans with a higher fatty acid glycidyl (CGCs), and the adsorption of Cu²⁺ was examined on ethylenediamine tetraacetic acid dianhydride modified CGCs (EDTA‐CGCs) synthesized by the reaction of the CGCs with ethylenediamine tetraacetic acid dianhydride. The adsorption of phosphate ions onto the resulting substrate/metal‐ion complex was measured. Mo⁶⁺ depicted remarkable adsorption toward the CGCs, although all the Mo⁶⁺ was desorbed under the adsorption conditions of the phosphate ions. The other metal ions were adsorbed to some extent on CGCs by chelating to the amino group in the substrate, except for CGC‐1, which had the highest degree of substitution (83.9%). Considerable amounts of Fe²⁺ were adsorbed onto CGCs; however, only a limited number of phosphate ions was adsorbed onto the substrate/metal‐ion complex. As a result, the following adsorbent/metal‐ion complexes gave higher adsorption ability toward phosphate ions: CGC‐4/Cu²⁺, CGC‐4/Fe³⁺, and EDTA‐CGC‐3/Fe³⁺. Where, CGC‐3 is a chemically modified chitosan with the degree of substitution of 26.5 percentage, and CGC‐4 is one with the degree of substitution of 16.0 percentage. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of A‐ or B‐site doping of perovskite calcium manganite on structure,resistivity, and thermoelectric properties

Bismuth‐, lanthanum‐, and molybdenum‐doped calcium manganite (CaMnO₃, abbreviated Mn113) are synthesized by solid‐state synthesis route from their respective oxide precursors at a same doping level (x=0.05). Depending on the ionic sizes, trivalent dopants (Bi³⁺ and La³⁺) replace Ca²⁺(A site), while penta/hexavalent dopant Mo⁵⁺/Mo⁶⁺ replaces Mn⁴⁺ (B site) in the Mn113 structure. XRD of all three doped samples confirm formation of single phase. In all three samples, doping causes unit cell volume to expand, while volume expansion is maximum for the Mo‐Mn113. The transport behavior of the doped samples follows small polaron hopping mechanism. Resistivity of the doped samples depends not only on the carrier concentration but also on the effective bandwidth determined by the structural distortion introduced by the dopant ions. Bi‐Mn113 has highest resistivity at the both temperature end, while La‐Mn113 has the lowest. Thermopower is determined by the carrier concentration only and does not depend on dopant type, having value ~260 μV/K at 1000 K. At high (>800 K), S reaches a saturation value and becomes independent of T. La‐Mn113 is having highest figure of merit (zT) 0.19 at 1000 K.     

Photo Catalytic Degradation of Imidachloprid Under Solar Light Using Metal Ion Doped TiO2 Nano Particles: Influence of Oxidation State and Electronic Configuration of Dopants

Anatase TiO₂ was doped with metal ions like Th⁴⁺, V⁵⁺ and Mo⁶⁺ and tested for the degradation of imidachloprid under solar light. X-ray diffraction results inferred that all the dopants stabilized the anatase phase irrespective of their nature, oxidation state and ionic size. The undoped and transition metal ion doped TiO₂ were completely transformed to rutile phase at 700 °C while rare earth Th⁴⁺ doped sample completely transformed to rutile phase at 1,000 °C. The rare earth dopant stabilized the anatase phase by hindering the growth of crystallite size. Among the photo catalysts used, Th⁴⁺ (0.06%)-TiO₂ showed highest activity and its efficiency was 2.8 times higher than that of Degussa P-25. The Th⁴⁺ ion lowered the band gap of TiO₂ to 2.6 and 2.5 eV facilitating solar light absorption. Detrapping of the trapped charge carriers depends on electronic configuration and the oxidation state of the dopants.     

Shielding Behavior of Gamma-Irradiated MoO<Subscript>3</Subscript> or WO<Subscript>3</Subscript>-Doped Lead Phosphate Glasses Assessed by Optical and FT Infrared Absorption Spectral Measurements

Undoped and MoO₃- or WO₃- doped lead phosphate glasses were prepared by the melting-annealing technique. The glasses were characterized through UV-visible and infrared measurements which were repeated after gamma irradiation. Optical spectrum of binary lead phosphate glass shows distinct ultraviolet bands correlated with unavoidable trace iron impurities within the chemicals used for the preparation of the glasses. UV-visible absorption spectra of MoO₃- or WO₃- doped glasses exhibit additional UV-visible bands which are related to the presence of four oxidation states of the two transition metal (molybdenum or tungsten) ions (Mo³⁺, Mo⁴⁺, Mo⁵⁺, Mo⁶⁺, W³⁺, W⁴⁺, W⁵⁺, W⁶⁺). The extra UV band is related to hexavalent (5d⁰) state while the rest of the visible bands are related to (350–440 nm - trivalent state), (450, 550, 650 nm - tetravalent state) while the broad band centered at about 770 nm (pentavalent state). The intensities of the absorption bands are observed to change with the transition metal content and their valencies. Infrared absorption spectra reveal distinct vibrational bands which are assigned to phosphate groups with sharing of Pb-O vibrations within both the range 460–620 cm^-1 and the range 900–1100 cm^-1 revealing a compact network structure. Gamma irradiation causes a minor increase in intensity of one of the UV band due to suggested photo-oxidation of some trace ferrous ions to additional ferric ions but the remaining spectral curve remains unaffected which is obviously related to some shielding effects of heavy atomic weight of PbO. This heavy metal oxide (PbO) is assumed to retard or prohibit the free passage of free electrons or positive holes generated during the irradiation process.     

Effect of Ni<Superscript>2+</Superscript>, V<Superscript>4+</Superscript> and Mo<Superscript>6+</Superscript> concentration on iron oxidation by <Emphasis Type="Italic">Acidithiobacillus ferrooxidans</Emphasis>

The ferrous oxidation ability of Acidithiobacillus ferrooxidans was studied in the presence of Ni²⁺, V⁴⁺ and Mo⁶⁺ in 9 K media in order to implement the culture in the bioleaching of spent catalyst. The rate of iron oxidation decreased with increasing concentration of metal ions, but the rate of inhibition was metal-ion dependent. The tolerance limit was critical at a concentration of 25 g/L Ni²⁺, 5 g/L V⁴⁺ and 0.03 g/L Mo⁶⁺. The growth rate of microorganisms was negligible at concentrations of 6 g/L V⁴⁺ and 0.04 g/L Mo⁶⁺. Levels and degree of toxicity of these ions have been quantified in terms of a toxicity index (TI). The toxicity order of metal ions was found to be Mo⁶⁺>V⁴⁺>Ni²⁺. The significance and relevance of multi-metal ion tolerance in Acidithiobacillus ferrooxidans has been highlighted with respect to bioleaching of spent refinery catalyst.     

Structure-property relations of co-doped bismuth layer-structured Bi3.25La0.75(Ti1-xMox)3O12 ceramics

In this work, the fabrication and investigation of substituting higher-valence Mo⁶⁺ for Ti⁴⁺ ion on the B-site of La³⁺-doped Bi₄Ti₃O₁₂ [BLT] structure to form Bi_3.25La_0.75(Ti_1-x Mo _x )₃O₁₂ [BLTM] (when x = 0, 0.01, 0.03, 0.05 0.07, 0.09, and 0.10) ceramics were carried out. X-ray diffraction patterns of BLTM ceramics indicated an orthorhombic structure with lattice distortion, especially with a higher concentration of a MoO₃ dopant. Microstructural investigation showed that all ceramics composed mainly of plate-like grains. An increase in MoO₃ doping content increased the length and thickness of the grain but reduced the density of the ceramics. Electrical conductivity was found to decrease, while the dielectric constant increased with Mo⁶⁺ doping concentration. Ferroelectric properties were found to be improved with increasing MoO₃ content and were optimized at x = 0.1.     

Structure stability,bond characteristics and microwave dielectric properties of co-substituted NdNbO4 ceramics

Structure-property relationship of co-substituted (Mg²⁺_1/4Mo⁶⁺_3/4)⁵⁺, (Al³⁺_1/3Mo⁶⁺_2/3)⁵⁺, (Si⁴⁺_1/2Mo⁶⁺_1/2)⁵⁺, (Zr⁴⁺_1/2Mo⁶⁺_1/2)⁵⁺ for Nb⁵⁺ in NdNbO₄ ceramics was investigated systematically. The remarkable differences in dielectric properties of each composition originated from their bond characteristics and structure stability. The elongated/compressed bonds have an effect on the cell volume and polarization. And the average bond covalency of Nb-O bond was responsible for the development of permittivity. Q×f values and the total lattice energy went up to maximum when (Si_0.5Mo_0.5) occupied Nb-site. Variations of lattice energy together with Nb-O bond energy suggest that a more stable structure was obtained through co-substitution. The optimal microwave dielectric properties is: ε_r =?18.97, Q×f?=?49466?GHz, τ_f =?7.34?ppm/°C for NdNb_0.97(Si_0.5Mo_0.5)_0.03O₄, sintered at 1250?°C.     

Sol–gel synthesis of Nd-doped BiFeO3 multiferroic and its characterization

Neodymium doped bismuth ferrite (BiFeO₃, BFO) nanoparticles were successfully synthesized by a facile sol–gel route. The influence of annealing temperature, time, Bi content and solvent on the crystal structure of BFO was studied. Results indicated that the optimum processing condition of BFO products was 550–600 °C/1.5 h with excess 3–6% Bi and ethylene glycol as solvent. On the other hand, Nd³⁺ ion was introduced into the BFO system and the effect of Nd³⁺ concentration on the structure, magnetic and dielectric properties of BFO were investigated. It was found that the magnetization of BFO was enhanced significantly with Nd³⁺ substitution, being attributed to the suppression of the spiral cycloidal magnetic structure led by the crystal structure transition. Furthermore, with increasing Nd³⁺ content, the dielectric constant was found to decrease while the dielectric loss was enhanced, which was mainly due to the hoping conduction mechanism with the reduction of oxygen vacancies.     

Sintering and properties of molybdenum-doped SrBi2Ta2O9 ceramics

The effects of molybdenum doping on the sintering, microstructure, dielectric properties, and ferroelectric properties of SrBi₂(Ta_1−xMo_x)O_9+y ceramics were investigated. The densification process of the molybdenum doped ceramics with x=0.025–0.1 can be shifted to a lower temperature range. When the degree of densification is nearly the same, the doped ceramics showed reduced dielectric constant as compared with the undoped ceramics. For the ceramics with relative density ⩾90%, the dielectric constant is 120–125 and 80–120 for the undoped and doped ceramics, and the dielectric loss tangent is below 2%. For nearly the same relative density, all the molybdenum-doped ceramics have significantly increased P_r and decreased E_C as compared with the undoped ceramics. There are optimum molybdenum content (x=0.025–0.05) and optimum sintering temperature (1100 °C) for maximum P_r and minimum E_C.     

Multifunctionality of Active Centers in (Amm)oxidation Catalysts: From Bi–Mo–O x to Mo–V–Nb–(Te, Sb)–O x

Catalytic centers in selective (allylic) oxidation and ammoxidation catalysts are multimetallic and multifunctional. In the historically important bismuth molybdates, used for propylene (amm)oxidation, they are composed of (Bi³⁺)(Mo⁶⁺)₂ complexes in which the Bi³⁺ site is associated with the -H abstraction and the (Mo⁶⁺)₂ site with the propylene chemisorption and O or NH insertion. An updated reaction mechanism is presented. In the Mo–V–Nb–Te–O _x systems, three crystalline phases (orthorhombic Mo_7.5V_1.5NbTeO₂₉, pseudohexagonal Mo₆Te₂VO₂₀, and monoclinic TeMo₅O₁₆) were identified, with the orthorhombic phase being the most important one for propane (amm)oxidation. Its active centers contain all necessary key catalytic elements (2V⁵⁺/Mo⁶⁺, 1V⁴⁺/Mo⁵⁺, 2Mo⁶⁺/Mo⁵⁺, 2Te⁴⁺) for this reaction wherein a V⁵⁺ surface site (V⁵⁺ = O ⁴⁺V–O) is associated with paraffin activation, a Te⁴⁺ site with -H abstraction once the olefin has formed, and a (Mo⁶⁺)₂ site with the NH insertion. Four Nb⁵⁺ centers, each surrounded by five molybdenum octahedra, stabilize and structurally isolate the catalytically active centers from each other (site isolation), thereby leading to high selectivity of the desired acrylonitrile product. A detailed reaction mechanism of propane ammoxidation to acrylonitrile is proposed. Combinatorial methodology identified the nominal composition Mo_0.6V_0.187Te_0.14Nb_0.085O _x for maximum acrylonitrile yield from propane, 61.8% (86% conversion, 72% selectivity at 420 °C). We propose that this system, composed of 60% Mo_7.5V_1.5NbTeO₂₉, 40% Mo₆Te₂VO₂₀, and trace TeMo₅O₁₆, functions with a combination of compositional pinning of the optimum orthorhombic Mo_7.5V_1.5±x Nb_1±y Te_1±z O_29± phase and symbiotic mop-up of olefin intermediates through phase cooperation. Under mild reaction conditions, a single optimum orthorhombic composition might suffice as the catalyst; under demanding conditions this symbiosis is additionally required. Improvements in catalyst performance could be attained by further optimization of the elemental distributions at the active catalytic center of Mo_7.5V_1.5NbTeO₂₉, by promoter/modifier substitutions, and incorporation of compatible cocatalytic phases (preferably epitaxially matched). High-throughput methods will greatly accelerate the rational catalyst design processes.     

Influence of Nb2O5 addition on dielectric properties and diffuse phase transition behavior of BaZr0.2Ti0.8O3 ceramics

Nb₂O₅ doped Ba(Zr_0.2Ti_0.8)O₃ (short as BZT20) ceramics were prepared by a mixed-oxide method using a high-energy planetary ball mill and the influence of Nb₂O₅ addition on microstructure, dielectric properties and diffuse phase transition behavior of BZT20 ceramics were investigated. It was demonstrated that Nb⁵⁺entered the B-site of BZT20 ceramic and substituted for Ti⁴⁺, which caused the expansion and distortion of crystal lattice. BZT20 ceramics doped with 0.2 mol% Nb₂O₅ showed excellent dielectric property and lower diffusivity with ε_m=37,823 and γ=1.49. We supposed that the increase of dielectric constant and decrease of diffuseness parameter with increasing Nb₂O₅ content were caused by lattice disorder and unbalancing of cations induced by the substitution of Ti⁴⁺ by Nb⁵⁺ in the B sites of BZT20 ceramics. The Curie temperature decreased with the increase of Nb₂O₅ content, which can be attributed to enlarged distortion energy of the Nb doped BZT20 structure. Besides, grain size effect on the dielectric property and diffuse phase transition behavior of Nb₂O₅ doped BZT20 ceramics was also investigated.     

Synthesis and characterization of low CTE value La2O3-B2O3-CaO-P2O5 glass/cordierite composites for LTCC application

Low-softening-point La₂O₃-B₂O₃-CaO-P₂O₅ (LBCP) glass-ceramic/cordierite composite systems have been prepared in this work. Influence of the ratio of La₂O₃ to B₂O₃ and the content of cordierite on the sintering behavior, microstructure, sintering quality, thermal properties and dielectric properties of composites are studied. The results show that high La₂O₃/B₂O₃ ratio improves the crystalline quality of LBCP glass-ceramic, but also narrows its process window. The increase of cordierite content reduces the coefficient of thermal expansion (CTE) value of composites obviously. However, excess cordierite is detrimental to the densification of the composite microstructure, and too low cordierite content causes serious foaming. Sample containing 30?wt% LBCP1 glass-ceramic and 70?wt% cordierite sintered at 850?°C shows excellent properties: relative density of 95.26%, CTE value of 4.12?ppm/°C, dielectric constant of 4.78 (1?MHz)/4.52 (12.8?GHz), dielectric loss of 2.3?×?10^?3 (1?MHz)/2.5?×?10^?3 (12.8?GHz) and the ability to co-fire with silver, which suggests that LBCP glass/cordierite composite system has potential to meet the requirements of LTCC substrate material.     

Poly(2‐acrylamido glycolic acid‐co‐2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid): Synthesis,characterization, and retention properties for environmentally impacting metal ions

Poly(2‐acrylamido glycolic acid‐co‐2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid) [P(AGA‐co‐APSA)] was synthesized by radical polymerization in an aqueous solution. The water‐soluble polymer, containing secondary amide, hydroxyl, carboxylic, and sulfonic acid groups, was investigated, in view of their metal‐ion‐binding properties, as a polychelatogen with the liquid‐phase polymer‐based retention technique under different experimental conditions. The investigated metal ions were Ag⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, and Cr³⁺, and these were studied at pHs 3, 5, and 7. P(AGA‐co‐APSA) showed efficient retention of all metal ions at the pHs studied, with a minimum of 60% for Co(II) at pH 3 and a maximum close to 100% at pH 7 for all metal ions. The maximum retention capacity (n metal ion/n polymer) ranged from 0.22 for Cd²⁺ to 0.34 for Ag⁺. The antibacterial activity of Ag⁺, Cu²⁺, Zn²⁺, and Cd²⁺ polymer–metal complexes was studied, and P(AGA‐co‐APSA)–Cd²⁺ presented selective antibacterial activity for Staphylococcus aureus with a minimum inhibitory concentration of 2 μg/mL. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The NbO6 octahedral distortion and phase structural transition of Eu3+‐doped K0.5Na0.5NbO3–xLiNbO3 ferroelectric ceramics

A small quantity of Eu³⁺ ions were doped in the lead‐free ferroelectric K_0.5Na_0.5NbO₃–xLiNbO₃ (KNN–xLN, 0 ≤ x ≤ 0.08) ceramics to investigate the NbO₆ octahedral distortion induced by the increasing LN content. In addition, the phase structure, ferroelectric, and photoluminescence properties of K_0.5Na_0.5NbO₃–xLiNbO₃:0.006Eu³⁺ (KNN–xLN:0.006Eu³⁺) lead‐free piezoelectric ceramics were characterized. All the X‐ray diffraction, Raman spectra, dielectric constant vs temperature measurements and the photoluminescence of Eu³⁺ ions demonstrated that the prepared ceramics undergo a polymorphic phase transition (PPT, from orthorhombic to tetragonal phase transformation) with the rising LN content, and the PPT region locates at 0.05 ≤ x ≤ 0.06. The ferroelectric properties, Raman intensity ratios and photoluminescence intensity ratios show similar variations with the increasing LN content, all with a maximum value achieved at the PPT region. We believe that the close relationship among the ferroelectric properties, Raman intensity ratios, and photoluminescence intensity ratios is caused by the NbO₆ octahedral distortion. The photoluminescence of Eu³⁺ ion was discussed basing on the crystal‐symmetry principle and Judd‐Ofelt theory.     

Synthesis,Structure and Electrical Properties of Mo‐doped CeO2–Materials for SOFCs

In this paper, we report the synthesis, structure and electrical conductivity of Mo‐doped compounds with a nominal chemical formula of Ce_1–xMo_xO_2+δ (x = 0.05, 0.07, 0.1) (CMO). The formation of fluorite‐like structure with a small amount of Ce₈Mo₁₂O₄₉ impurity (JCPDS Card No. 31‐0330) was confirmed using a powder X‐ray diffraction (PXRD). The fluoride‐type structure was retained under wet H₂ and CH₄ atmospheres at 700 and 800 °C, while diffraction peaks due to metal Mo were observed in dry H₂ under the same condition. AC impedance measurements showed that the total conductivity increases with increasing Mo content in CMO, and among the investigated samples, Ce_0.9Mo_0.1O_2+δ exhibited the highest electrical conductivity with a value of 2.8 × 10^–4 and 5.08 × 10^–2 S cm^–1 at 550 °C in air and wet H₂, respectively. The electrical conductivity was found to be nearly the same, especially at high temperatures, in air, O₂ and N₂. Chemical compatibility of Ce_0.9Mo_0.1O_2+δ with 10 mol‐% Y₂O₃ stabilised ZrO₂ (YSZ) and Ce_0.9Gd_0.1O_1.95 (CGO) oxide ion electrolytes in wet H₂ was evaluated at 800–1,000 °C, using PXRD and EDX analyses. PXRD showed that CMO was found to react with YSZ electrolyte at 1,000 °C. The area specific polarisation resistance (ASPR) of Ce_0.9Mo_0.1O_2+δ on YSZ was found to be 8.58 ohm cm² at 800 °C in wet H₂.     

High‐Q microwave ceramics of Li2TiO3 co‐doped with magnesium and niobium

In order to solve the problems of acceptor/donor individual doping in Li₂TiO₃ system and clarify the superiority mechanism of co‐doping for improving the Q value, Mg + Nb co‐doped Li₂TiO₃ have been designed and sintered at a medium temperature of 1260°C. The effects of each Mg/Nb ion on structure, morphology, grain‐boundary resistance and microwave dielectric properties are investigated. The substitution of (Mg_1/3Nb_2/3)⁴⁺ inhibits not only the diffusion of Li⁺ and reduction in Ti⁴⁺, but also the formation of microcracks in ceramics, which promotes the enhancement of Q value. The experiments reveal that Q × f value of Li₂TiO₃ ceramics co‐doped with magnesium and niobium is 113 774 GHz (at 8.573 GHz), which is increased by 113% compared with the pure Li₂TiO₃ ceramics. And the co‐doped ceramics have an appropriate dielectric constant of 19.01 and a near‐zero resonance frequency temperature coefficient of 13.38 ppm/°C. These results offer a scientific basis for co‐doping in Li₂TiO₃ system, and the outstanding performance of (Mg + Nb) co‐doped ceramics provides a solid foundation for widespread applications of microwave substrates, resonators, filters and patch antennas in modern wireless communication equipments.     

Multi-electrochromism behavior and electrochromic mechanism of electrodeposited molybdenum doped vanadium pentoxide films

Molybdenum doped vanadium pentoxide (Mo doped V₂O₅) films are prepared by cathodic electrodeposition on indium tin oxide substrate from Mo doped V₂O₅ sol. As an anodic and cathodic coloration electrochromic material, the electrodeposited Mo doped V₂O₅ film presents a better cycling stability, reversibility and multi-electrochromic behavior (orange-yellow-green-blue) with an optical modulation of 60-90% in the spectral region 550-900 nm, which can be expected as a result of enhanced electron intervalence transfer between Mo⁶⁺ and V⁵⁺, V⁴⁺ states, in addition to V⁵⁺ and V⁴⁺ transition. The electrochromic mechanism of Mo doped V₂O₅ films is investigated with atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy. The surface roughness of the film increase at the different coloration states due to the increasing crystallinity degree. The change of the interlayer spacing for the host V₂O₅ and the change of the C and Li element states verify the insertion of organic solvent into the interlayer of the host V₂O₅ and some of the Li⁺ ions into the sites in the V-O layers. The electrochromic kinetics process indicates that the electrochromism of Mo doped V₂O₅ films can be considered as a reversible reduction/oxidation process accompanying the insertion/extraction of Li⁺ ions and electrons.     

Studies on polycarbazole‐modified electrode and its applications in the development of solid‐state potassium and copper(II) ion sensors

Electrochemical synthesis of polycarbazole, having better stability and electrochromic activity, in dichloromethane containing 0.1 M tetrabutyl ammonium perchlorate (TBAP) is reported at 1.4 V versus Ag/AgCl. The electrochemistry based on cyclic voltammetric measurements in dichloromethane containing TBAP show redox behavior of the polymer associated to doping and de‐doping of ClO ion within the polymer interstices. The polycarbazole matrix obtained by the potentiostatic and potentiodynamic modes of electropolymerization is characterized based on scanning electron microscopy, differential calorimetry, and infrared spectroscopy. De‐doping of the polymer is studied by electrochemical reduction in TBAP‐free dichloromethane followed by incubation of the polymer film in 1 M aqueous KCl solution for 24 h. The open circuit potential (OCP) of doped and de‐doped polycarbazole modified electrode under the present experimental conditions is found to 462 and 19 mV, respectively, versus SCE in 0.1 M NH₄NO₃. The de‐doped polymer shows remarkable sensitivity and selective to Cu(II) ion compared to its sensitivity for Fe³⁺, Ni²⁺, Co²⁺, Pb²⁺, and Cu⁺ ions. A typical response of the de‐doped polymer electrode to Cu(II) ion is reported. On the other hand, ClO doped polymer is used in the development of solid‐state K⁺ ion sensors using dibenzo‐18‐crown‐6/valinomycin as a neutral carrier–based, plasticized poly vinyl chloride matrix membrane assembled over a polymer‐modified electrode. The doped polymer under this condition helps in maintaining charge stabilization across Pt/polymer and polymer/PVC interfaces. The lowest detection limit for the potassium ion sensor is 5 × 10⁻⁵ M with a slope of 58 mV/decade for valinomycin‐based sensor and 6.8 × 10⁻⁵ M with a slope of 54 mV for dibenzo‐18‐crown‐6 carriers with a wide linearity. The typical potentiometric results on the sensitivity, detection limits, and OCP to K⁺ ion recorded using present polymer are compared with the data recorded earlier using polyindole and a similar neutral carrier–based PVC membrane. A comparison on electrode kinetics of these two polymer‐modified electrodes also has been made using the data on Tafel plots to study the relative kinetic polarizability based on ion‐exchange currents. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1749–1759, 2000     

Complex Effect of Sm3+/W6+ Codoping on α‐β Phase Transformation and Phonon Scattering of Oxygen‐Deficient La2Mo2O9

Lanthanum molybdate, La₂Mo₂O₉, has been attracted considerable attention owing to its high concentration of intrinsic oxygen vacancies, which could be reflected by enhanced phonon scattering and low thermal conductivity. A new series of La₂Mo₂O₉‐based oxides of the general formula La_2?xSm_xMo_2?xW_xO₉, where x ≤ 0.2, were synthesized by citric acid sol–gel process. The variation in thermal conductivity with Sm³⁺and W⁶⁺ fractions was analyzed based on structure information provided by X‐ray diffraction and Raman spectroscopy. The fully dense La_2?xSm_xMo_2?xW_xO₉ ceramics showed a minimum thermal conductivity value [κ = 0.84 W·(m·K)^?1,T = 1073 K] at the composition of La_1.8Sm_0.2Mo_1.8W_0.2O₉, which stems from the multiple enhanced phonon scatterings due to mass and strain fluctuations at the La³⁺ and Mo⁶⁺ sites as well as the high concentration of intrinsic oxygen vacancies embedded in the crystal lattice. The thermal conductivities present an abrupt decrease at the structural transition, which is due to the phase transformation from a low‐temperature ordered form (monoclinic α‐La₂Mo₂O₉) to a high‐temperature disordered form (cubic β‐La₂Mo₂O₉₎.