Crystal structure and ionic conductivity of Mg-doped apatite-type lanthanum silicates La10Si6-x Mgx O27-x（x=0–0.4）

Lanthanum silicates La10Si6-xMgxO27-x(x = 0–0.4) were prepared by solid state synthesis to investigate the effect of Mg doping on crystal structure and ionic conductivity. Rietveld analysis of the powder XRD patterns reveals that Mg substitution on Si site results in significant enlargement of channel triangles, favoring oxide-ion conduction. Furthermore,an increase of Mg concentration significantly influences the linear density of interstitial oxygen, which plays an important role in ionic conductivity. The Arrhenius plots of La10Si6-xMgxO27-x(x = 0–0.4) suggest that Mg-doped samples present higher conductivity and lower activation energy than non-doped La10Si6O27, and La10Si5.8Mg0.2O26.8exhibits the highest conductivity with a value of 3.0×10-2S ·cm-1at 700?C. Such conductive behavior agrees well with the refined results.The corresponding mechanism has been discussed in this paper.     

High-quality CdS quantum dots sensitized ZnO nanotube array films for superior photoelectrochemical performance

The surface characteristics of ZnO were synthetically optimized by a self-designed simultaneous etching and W-doping hydrothermal method utilizing as-prepared ZnO nanorod (NR) array films as the template. Benefiting from the etching and regrowth process and the different structural stabilities of the various faces of ZnO NRs, the uniquely etched and W-doped ZnO (EWZ) nanotube (NT) array films with larger surface area, more active sites and better energy band structure were used to improve the photoelectrochemical (PEC) performance and the loading quality of CdS quantum dots (QDs). On the basis of their better surface characteristics, the CdS QDs were uniformly loaded on EWZ NT array film with a good coverage ratio and interface connection; this effectively improved the light-harvesting ability, charge transportation and separation as well as charge injection efficiency during the PEC reaction. Therefore, all the CdS QD-sensitized EWZ NT array films exhibited significantly enhanced PEC performance. The CdS/EWZ-7 composite films exhibited the optimal photocurrent density with a value of 12 mA· cm^-2, 2.5 times higher than that of conventional CdS/ZnO-7 composite films under the same sensitization times with CdS QDs. The corresponding etching and optimizing mechanisms were also discussed.     

In-situ fabrication of ZnO nanoparticles sensors based on gas-sensing electrode for ppb-level H_2S detection at room temperature

The zinc oxide(ZnO)nanoparticles(NPs)sensors were prepared in-situ on the gas-sensing electrodes by a one-step simple sol-gel method for the detection of hydrogen sulfide(H₂S)gas.The sphere-like ZnO NPs were characterized by scanning electron microscopy(SEM),transmission electron microscopy(TEM),x-ray diffraction(XRD),energy dispersive x-ray analysis(EDX),and their H₂S sensing performance were measured at room temperature.Testing results indicate that the ZnO NPs exhibit excellent response to H₂S gas at room temperature.The response value of the optimal sample to750 ppb H₂S is 73.3%,the detection limit reaches to 30 ppb,and the response value is 7.5%.Furthermore,the effects of the calcining time and thickness of the film on the gas-sensing performance were investigated.Both calcining time and film thickness show a negative correlation with the H₂S sensing performance.The corresponding reaction mechanism of H₂S detection was also discussed.     

Crystal structure and ionic conductivity of Mg-doped apatite-type lanthanum silicates LaloSi6-xMgxO27-x （x= 0-0.4）

Lanthanum silicates LaloSi6 xMgxO27_x （x = 0-0.4） were prepared by solid state synthesis to investigate the effect of Mg doping on crystal structure and ionic conductivity. Rietveld analysis of the powder XRD patterns reveals that Mg substitution on Si site results in significant enlargement of channel triangles, favoring oxide-ion conduction. Furthermore, an increase of Mg concentration significantly influences the linear density of interstitial oxygen, which plays an important role in ionic conductivity. The Arrhenius plots of LaloSi6_xMgxO27 x （x = 0-0.4） suggest that Mg-doped samples present higher conductivity and lower activation energy than non-doped La10Si6027, and LaloSis.8Mgo.2026.8 exhibits the highest conductivity with a value of 3.0× 10-2 S .cm 1 at 700 ℃. Such conductive behavior agrees well with the refined results. The corresponding mechanism has been discussed in this paper.     

Low-temperature synthesis of apatite-type La_(9.33)Ge_6O_(26) as electrolytes with high conductivity

In the present study,high-quality apatite-type La_(9.33)Ge_6O_(26) powders are successfully synthesized by a facile moltensalt synthesis method(MSSM) at low temperatures,using Li Cl,Li Cl/Na Cl mixture(mass ratio 1:1) as molten salt,respectively.Experimental results indicate that the optimal mass ratio between reactant and molten salt is 1:2,and Li Cl/Na Cl mixed molten-salt is more beneficial for forming high-quality La_(9.33)Ge_6O_(26) powders than Li Cl individual molten-salt.Comparing with the conventional solid-state reaction method(SSRM),the synthesis temperature of apatitetype La_(9.33)Ge_6O_(26) powders using the MSSM decreases more than 350?C,which can effectively avoid Ge loss in the preparation process of precursor powders.Furthermore,the powders obtained by the MSSM are homogeneous,nonagglomerated and well crystallized,which are very favorable for gaining dense pellets in the premise of avoiding Ge loss.On the basis of high-quality precursor powders,the dense and pure ceramic pellets of La_(9.33)Ge_6O_(26) are gained at a low temperature of 1100?C for 2 h,which exhibit higher conductivities(σ850?C(Li Cl)= 2.3 × 10~(-2) S·cm~(-1),σ850 ?C(Li Cl/Na Cl) = 4.9 × 10~(-2) S·cm~(-1)) and lower activation energies(Ea(Li Cl)= 1.02 e V,Ea(Li Cl/Na Cl)= 0.99 e V) than that synthesized by the SSRM.     

Pressure-induced structural evolution of apatite-type La_(9.33)Si_6O_(26)

The pressure-induced structural evolution of apatite-type La_(9.33)Si_6O_(26) was systematically studied using in situ synchrotron x-ray diffraction(XRD). The XRD spectra indicated that a subtly reversible phase transition from P6_3/m to P6_3 symmetry occurred at ～ 13.6 GPa because of the tilting of the SiO_4 tetrahedra under compression. Furthermore, the La_(9.33)Si_6O_(26) exhibited a higher axial compression ratio for the a-axis than the c-axis, owing to the different axial arrangement of the SiO_4 tetrahedra. Interestingly, the high-pressure phase showed compressibility unusually higher than that of the initial phase, suggesting that the low P63 symmetry provided more degrees of freedom. Moreover, the La_(9.33)Si_6O_(26) exhibited a lower phase transition pressure(PT) and a higher lattice compression than La_(10)Si_6O_(27). Comparisons between La_(9.33)Si_6O_(26) and La_(10)Si_6O_(27) provided a deeper understanding of the effect of interstitial oxygen atoms on the structural evolution of apatite-type lanthanum silicates(ATLSs).