Crystal structure of dehydrated LiNa-A type zeolites

The crystal structures of dehydrated Li-exchanged A-type zeolites, determined by neutron and X-ray diffraction powder methods, indicate that the majority of the Li-cations are located at the six-ring centres. The framework distortion is progressive from d-K-A to d-Na-A and d-Li-A and follows the charge to radius ratio of the exchangeable cations. The shape of the framework eight-rings changes accordingly.     

Ionic conductivity in samarium-doped NaCl

A study of ionic conductivity as a function of temperature has been carried out in NaCl and NaCl doped with 0.5 and 1.0 mol% samarium. The conductivity-temperature plot of NaCl exhibits a well-known three-stage conductivity in the temperature range 100 to 650° C. The knee separating intrinsic and extrinsic regions is at a temperature of about 525° C. The conductivity-temperature plots of samarium-doped NaCl exhibit three-stage extrinsic (II, III and IV) conductivity in the temperature range 100 to 525° C. The intrinsic region I, was not observed in these plots, as the conductivity measurements were taken up to 525° C. From the analysis of these plots activation energies for the migration of cation vacancy, the formation of Schottky pairs, the association of the samarium ion with a cation vacancy and the dilution of samarium ions in the lattice of NaCl are calculated. These values are compared with previously reported ones.     

Ionic conductivity in wide-range halide-pyrophosphate glasses

Recently we have reported the existence of fast ionic conduction in silver halide-rich all-halide glasses. In the present paper we report glass formation from x = 0.08−1.0 in a pseudobinary halide-pyrophosphate system x(AgCl)_0.64(CsI)_0.36 + (1−x)(Ag₂PO_3.5) and study the composition dependence of the conductivity. Glass transition temperatures and activation energies for d.c. conductivity increases smoothly as the pyrophosphate concentration increases, while the conductivity correspondingly decreases. The frequency dependence of the conduction process has been analysed. The conductivity relaxation process becomes increasingly non-exponential as the conductivity at some fixed temperature (eg. 298 K) increases.     

Ionic conductivity of fluoroaluminoindate glasses

(54 - 2.4x)InF₃ + xA1F₃ + (36 -1.6x)BaF₂ + 3xPbF₂ + 1OLiF glasses (nine compositions,x varying from 0 to 18 mol % at 2.25 mol % intervals) were prepared. The glass compositions were taken between the 60InF₃ + 40BaF₂ and 25A1F₃ + 75 PbF₃ eutectics, of which the former is glass-forming (10 mol % LiF was added for glass stabilization). The electrical properties of the glasses were studied by impedance spectroscopy at frequencies from 5 Hz to 500 kHz and temperatures from 20 to 200‡C. The 400-K ionic conductivity of the glasses was found to rise from 4.3 x 10^-6 S/cm in the PbF₂-free glass to 1.4 x 10^-5 S/cm in the glass containing 54 mol % PbF₂; concurrently, the 300-K static dielectric permittivity increases from 17 to 29.     

Positions of cations and molecules in zeolites with the mordenite-type framework II dehydrated hydrogen-ptilolite

A single crystal of natural ptilolite was ion-exchanged with NH₄⁺, heated to 320°C, sealed in a capillary at temperature, and the crystal structure was refined to R=0.048. Upon heating, NH₃ and H₂O were expelled and hydrogen condensed with framework oxygens. A strong correlation between T-O-T angle and the perturbation of T-O distances in adjacent tetrahedra is very similar to that in dehydrated-Ca-mordenite and is consistent with similar correlations in feldspar which were attributed to molecular-orbital effects. After adjustment for this correlation, mean T-O distances indicate slight Si, Al ordering. Remaining perturbations in T-O distances are small, and there is no convincing evidence for preferential attachment of protons to any particular framework oxygen. Some residual Na and K ions were located in site I at a twisted eight-ring. Two percent of the rings are not correctly stacked in Cmcm.     

Positions of cations and molecules in zeolites with the mordenite-type framework VII dehydrated cesium mordenite

Natural mordenite was ion-exchanged with CsCl solution and dehydrated at 300°C. The crystal structure [$\text{a}$ 18.194(19) $\text{b}$ 20.470(17) $\text{c}$ 7.506(9): Cs₇₄Al～₈Si～₄₀O₉₆] probably belongs to space group P2₁cn but was refined in the average space group Cmcm. Site occupancies for Cs are site II 3.8, IV 1.9, VI 1.8 atoms. Combined occupancies of sites IV and VI are less than 4 in dK-, dRb- and dCs- varieties. Cations larger than 1.3Å have not been found in site I. Cations in site VI block diffusion of large molecules in the main channel, and conversion of Na-mordenite from small-port to large-port variety by “decationization” towards H-mordenite might be explained by emptying sites IV and VI while up to 4 Na could remain in site I.     

Positions of cations and molecules in zeolites with the mordenite-type framework: V dehydrated Rb-mordenite

Mordenite from Challis Valley, Idaho, was ion-exchanged with RbCl₂ solution to ～Rb₈Al₈Si₄₀O₉₆·nH₂O. After dehydration at 340°C for 1 day, the crystal structure was determined at room temperature. Earlier attempts to dehydrate crystals at higher temperature led to disintegration, and even the present crystal fractured. Although this resulted in poor X-ray data, refinement in Cmcm ($\text{a}$ 18.127(7) $\text{b}$ 20.408(6) $\text{c}$ 7.463(3)Å) yielded atomic positions similar to those for dehydrated K-mordenite. Rb atoms in sites II (3.7Rb), IV (3.1Rb) and VI (0.7Rb) block most of the small channels (“side pockets”) and may hinder diffusion along the main channels. A few diffractions violating the C lattice were ignored in the refinement but indicate structural distortion similar to that in dehyrated K-mordenite which was refined in Pbcn. However the presence of a few weak diffractions violating the $\text{b}$ glide indicates even lower symmetry.     

Positions of cations and molecules in zeolites with the mordenite-type framework VI dehydrated barium mordenite

Natural mordenite was ion-exchanged with Ba(NO₃)₂ solution and dehydrated at 300°C. The crystal structure ($\text{a}$ 17.974(7) $\text{b}$ 20.320(8) $\text{c}$ 7.419(4)Å; Pbcn; electron microprobe analysis Ca_0.35Ba_3.3Al_8.6 Si_39pre9O_post96 has all the cations in the “side pocket” (site I, 0.3Ca; II, 1.9Ba; III, 0.3Ba; IV, 1.1Ba). No cations were located in the main channels, but the type IV cations lie in 8-rings of the channel walls. For charge balance, 1.2H are needed.     

Positions of cations and molecules in zeolites with the mordenite-type framework I dehydrated Ca-exchanged ptilolite

The crystal structure of dehydrated Ca-exchanged ptilolite has 4 sites for Ca: one each in twisted and near-circular 8-rings, one on the wall of the main channel, and one in a boat-shaped pocket in a zig-zag channel. Hindrance but not blocking of molecules could occur. The TO distances correlate inversely with TOT angles, consistent with observations and molecular-orbital calculations for feldspar. Tetrahedral mean TO distances adjusted for this effect indicate strong but not complete Si, A$\text{|l}$ disorder. The Ca occupancy is consistent with simple electrostatic and geometrical arguments.     

Ionic conductivity of lithium phosphate-doped lithium orthosilicate

The ionic conductivities of samples of lithium orthosilicate containing up to 50 mole % of lithium phosphate have been measured by both a c and d c techniques. Results indicate a large enhancement in lithium ion conduction due to the presence of the phosphate, making these materials attractive candidates for use as solid electrolytes in applications such as battery systems.     

Positions of cations and molecules in zeolites with the mordenite-type framework X dehydrated calcium hydrogen mordenite

Prolonged acid treatment of natural mordenite (2M Hc1, 90°C, 2 months) did not remove 1.4Ca atoms which persisted in site I of the final product after dehydration at 300°C. Electron microprobe analysis showed no detectable reduction of Al/Si ratio, but the cell parameters at room temperature ($\text{a}$ 18.058(3) $\text{b}$ 20.297(3) $\text{c}$ 7.484(2)Å) are lower than for the dehydrated-deammoniated variety, and the mean T-O distance is lower (1.606 vs. 1.617Å). The O-T-O and T-O-T angles are closer generally to those of dehydrated Ca-mordenite than to dehydrated-deammoniated mordenite. Population refinement produced no evidence in favor of vacant tetrahedral sites, but technical considerations cause complications. The present data would not be inconsistent with earlier suggestions that Al is replaced by Si in tetrahedral sites.     

Ionic and electronic conductivity in some simple lithium salts

The electrical conductivity () and thermoelectric power (S) of Li₃VO₄, Li₃PO₄ and Li₃BO₃ solidified melts are presented in the temperature range from 415 K to the melting point of each solid. The ionic ( _i,) and electronic ( _e) contributions to have been separated over the entire temperature range with the help of a time-dependence study of the d.c. electrical conductivity. Superionic phases in all three solids have been observed below their melting points in which the conductivity is almost purely ionic. The value of the phase transition temperature below which the solid transforms from superionic to normal phase has been obtained. It has been shown that in the normal phase, these solids are mixed conductors. Data for the temperature variations of both _i, and _e are also presented and discussed.     

Ionic conductivity in Li5AlO4 and LiOH

The ionic conductivity and thermal properties of Li₅AlO₄ and LiOH have been measured in wet and dry environments. Results show that an endothermic reaction at ～ 415°C and an associated large increase in conductivity is observed both in Li₅AlO₄ in a wet environment and in LiOH. These features are not observed in Li₅AlO₄ prepared and examined in a dry environment. This suggests that the large conductivity increase in Li₅AlO₄ results from LiOH retained within the material. The reaction(s) for formation of LiOH within Li₅AlO₄ and the associated electrical changes appear to be reversible as the environment switches from wet to dry at high temperatures (? 450°C). There is a significant (> 1%) electronic contribution to the conductivity in these materials.     

Positions of cations and molecules in zeolites with the mordenite framework IX dehydrated H-mordenite via acid exchange

Nearly complete removal of cations was accomplished for natural mordenite by preliminary Na-exchange followed by exposure to 2M HCl for 1 month at 90°C. The electron microprobe analysis (atomic Si/Al 4.7) indicates no detectable extraction of Al. However the cell dimensions after dehydration at 300°C followed by cooling to room temperature ($\text{a}$ 18.178(7) $\text{b}$ 20.394(6) $\text{c}$ 7.488(4)Å) are lower than for “hydrogen-mordenite” prepared via an ammonium-exchanged intermediary ($\text{a}$ 18.223(7) $\text{b}$ 20.465(9) $\text{c}$ 7.531(4)Å). Furthermore the tetrahedral distances are smaller (T4 down 0.017?, T3 0.010, T1 0.008, T2 0.002). Diffractions from the HCl-treated mordenite are sharp, and the positional and population parameters are close to those for the de-ammoniated mordenite. The simplest interpretation is that treatment with HCl results in extraction of Al from tetrahedral sites into other positions in the crystal coupled with migration of Si so that a crystalline structure is retained: however, many subtle complications require cautious interpretation.     

六氟磷酸盐吡啶离子液体的合成及电导率研究

采用二溴丁烷和3-甲基吡啶(物质的量之比为1.0∶2.2)为原料,以异丙醇为溶剂,温度控制在70～80℃,反应4～6h,得到吡啶溴盐离子液体。用吡啶溴盐与六氟磷酸盐发生置换反应,搅拌反应4h,得到六氟磷酸盐吡啶离子液体。测定了[C4(MPy)2][PF6]2离子液体在有机溶剂中的电导率;及离子液体在不同溶剂、不同浓度、不同温度下的电导率。结果表明:溶液的电导率随着温度升高而增大;随着浓度的增大而增大。相同温度、浓度下,乙腈的电导率最大;环丁砜的电导率最小。     

Ionic conductivity of high-purity Gd-doped ceria solid solutions

The Ce_1−xGd_xO_2−δ (0.02 ≤ x ≤ 0.3) solid solutions with ∼30 ppm SiO₂ were prepared through the conventional mixed-oxide method from high-purity CeO₂ and Gd₂O₃ powders. The ionic conductivity (especially the grain boundary (GB) conduction) in this system was studied as a function of dopant content, over the temperature range of 250–750 °C in air, using an impedance spectroscopy. The GB impedance played an important role in the total conduction in the samples with low Gd content (usually x ≤ 0.1), but decreased sharply with increasing Gd content. Both the total and GB conductivities maximized at the composition x = 0.15, and this composition also had the lowest activation energies for the total and GB conduction. The maximum total conductivity at 700 °C, σ_t = 4.07 (Ω m)⁻¹ with the activation energy, E_t = 0.77 eV, was found for the composition x = 0.15.     

LiZnPO4-LnPO4体系离子导电性的研究

采用柠檬酸盐溶胶-凝胶法制备了低温相α-LiZnPO4和以LiZnPO4为基质稀土磷酸盐(LnPO4)掺杂的(LiZnPO4)1-x-(LnPO4)x(Ln3+=Nd3+、Sm3+、Er3+、X=0.1;Ln3+=La3+,X=0.1、0.2、0.4、0.6)的超细粉体并对它们进行DTA、TG和XRD的表征.讨论了室温下不同比例、不同稀土磷酸盐的掺杂对基质LiZnPO4离子导电率的影响.测试结果表明,LiZnPO4-LnPO4体系是由α-LiZnPO4和LnPO4两相组成;由于α-LiZnPO4烧结体的相对密度(d=58)极小,室温下样品几乎不显示导电性,而适量的非导电相LnPO4的掺入有助于提高烧结体的相对密度,增大体系的晶界电导率.