Mechanical and electrochemical properties of cubic and tetragonal LixLa0.557TiO3 perovskite oxide electrolytes

Solid oxide electrolytes with high Li ion conductivity and mechanical stability are vital for all solid-state lithium ion batteries. The perovskite material Li_xLa_0.557TiO₃ with various initial Li (0.303 ≤ x ≤ 0.370) is synthesized by traditional solid-state reaction. The cubic and tetragonal structures are prepared with fast and slow cooling, respectively. The results reveal that the Li ion conductivity of the cubic structure is higher. In fact, the bulk conductivity of 1.65 × 10^?3 S cm^?1 is obtained at room temperature for x = 0.350. The crystal structure is not affected by the Li₂O quantity. In addition, Young's modulus, hardness, and fracture toughness are determined with indentation method for both structures. The Young's modulus increases with increasing Li₂O. However, hardness and fracture toughness keep a relatively stable value independent of Li₂O quantity.     

Fabrication of all-solid-state battery using Li5La3Ta2O12 ceramic electrolyte

The chemical and electrochemical properties of Li₅La₃Ta₂O₁₂ (LLTa) solid electrolyte were extensively investigated to determine its compatibility with an all-solid-state battery. A well-sintered LLTa pellet with a garnet-like structure was obtained after sintering at 1200 °C for 24 h. Li ion conductivity of the LLTa pellet was estimated to be 1.3×10⁻⁴ S cm⁻¹. The LLTa pellet was stable when in contact with lithium metal. This indicates that Li metal anode, which is the best anode material, can be applied with the LLTa system. A full cell composed of LiCoO₂/LLTa/Li configuration was constructed, and its electrochemical properties were tested. In the resulting cyclic voltammogram, a clear redox couple of LiCoO₂ was observed, implying that the all-solid-state battery with the Li metal anode was successfully operated at room temperature. The redox peaks of the battery were still observed even after one year of storage in an Ar-filled glove-box. It can be concluded that the LLTa electrolyte is a promising candidate for the all-solid-state battery because of its relatively high Li ion conductivity and good stability when in contact with Li metal anode and LiCoO₂ cathode.     

Electrical properties of Li1.3Ge1.4Ti0.3Al0.3(PO4)3 superionic ceramics

Preparation and electrical characterization of NASICON-type compound, Li_1.3Ge_1.4Ti_0.3Al_0.3(PO₄)₃, are described. The solid solution is obtained with Ge⁴⁺ → Ti⁴⁺ and Ge⁴⁺ → Al³⁺ substitutions in LiGe₂(PO₄)₃. The powder has been fabricated by a solid state reaction and the structural characteristics of it have been studied by X-ray. Ceramic samples have been sintered by varying the sintering duration from 1 to 3 h. Samples were studied by complex impedance spectroscopy in the frequency range 1 MHz-1.2 GHz and temperature range 300-600 K. Two regions of relaxation dispersion were found. The dispersions were related to the fast Li⁺ ion transport in the grains and grain boundaries. Variation of the sintering duration has no considerable effect on electrical properties of the ceramics.     

Solid-state electrochromic devices with Nb2O5:Mo thin film and gelatin-based electrolyte

A gelatin-based electrolyte has been developed and characterized by impedance spectroscopy, X-ray diffraction, UV-vis-NIR spectroscopy and atomic force microscopy (AFM). The heat treatment temperature was found the key factor affecting its ionic conductivity that increases from 1.5 × 10⁻⁵ S/cm to 4.9 × 10⁻⁴ S/cm by heating from room temperature up to 80 °C. The temperature dependence of the ionic conductivity exhibits an Arrhenius behavior. EC-devices with the configuration K-glass/Nb₂O₅:Mo EC-layer/gelatin-based electrolyte/(CeO₂)_x(TiO₂)_1−x ion-storage (IS) layer/K-glass, have been assembled and characterized. They show a good long time cyclic stability, but the change of the optical density measured at 550 nm after 25 000 cycles was only 0.13.     

Influence of external electric field on relaxor behaviour of (Pb0.75Ba0.25)(Zr0.70Ti0.30)O3 ceramics

The effects of the external d.c. and a.c. electric field on the dielectric response and relaxor behaviour of lead–barium–zirconate–titanate (PBZT) ceramics of the composition Ba/Zr/Ti 25/70/30 have been studied. The significant influence of the strength of the d.c. bias field and the amplitude of the a.c. field on the dielectric constant maximum and frequency dispersion was determined. The magnitude of the dielectric response strongly decreases under the bias field and increases with the increase of the a.c. field amplitude. All parameters describing the relaxor behaviour of the studied ceramics changed under the external d.c. and a.c. electric field. The experimental results can be explained in terms of existing models of relaxors.     

Influence of lanthanum and niobium doping on the relaxor behaviour of (Pb0.75Ba0.25)(Zr0.70Ti0.30)O3 ceramics

The lead–barium–zirconate–titanate (PBZT) ceramics of composition (Ba/Zr/Ti: 25/70/30) exhibit classical relaxor ferroelectric behaviour similar to other complex lead perovskites such as lead–lanthanum–zirconate–titanate or lead–magnesium–niobiate. Influence of Nb or La admixture on grain structure, dielectric and pyroelectric properties was showed earlier. The effect of simultaneously lanthanum and niobium modified PBZT 25/70/30 ceramics on properties have been studied and compared with earlier results. The influence of the additives on the values of characteristic parameters describing the relaxor behaviour of the studied ceramics (ε^′_max, T_m, T_f, T_B) was determined.     

Dielectric and impedance spectroscopy of Bi(Ca0.5Ti0.5)O3 ceramic

Bismuth calcium titanate (BiCa_0.5Ti_0.5O₃) ceramic, fabricated by a ceramic processing technique, has been characterized using a variety of experimental techniques. Analysis of basic crystal structure using X-ray diffraction data exhibits the orthorhombic system. Measurements and detailed analysis of some electrical parameters (i.e.,dielectric constant, loss tangent (energy loss), electrical impedance and modulus, conductivity, etc.) of Bi(Ca_0.5Ti_0.5)O₃ in a wide range of frequency (10³–10⁶ Hz) and temperature (30–500 °C) have provided some interesting and useful data and results on structure–properties relationship, conduction mechanism, etc.The role of interface, space charge polarization and Maxwell–Wagner dielectric relaxation in getting high dielectric constant of the material at low frequencies and high temperatures has been discussed. Study of temperature dependence of Nyquist plots clearly shows the contributions of grains in resistive and capacitive properties of the material. The frequency of the applied electric field and temperature strongly affect the dielectric (permittivity and dissipation of energy) and electrical (impedance, electrical modulus and conductivity) characteristics of the material.     

Fabrication of Li2O-B2O3-P2O5 solid electrolyte by flame-assisted ultrasonic spray hydrolysis for thin film battery

Li₂O-B₂O₃-P₂O₅ glass soot was fabricated from aqueous precursor solution of a CH₃CO₂Li·2H₂O and BCl₃, POCl₃ by the flame-assisted ultrasonic spray hydrolysis. The aqueous precursor solution of the lithium acetates was first atomized with an ultrasonic vibrator (1.7 MHz). B₂O₃ and P₂O₅ were formed from BCl₃ and POCl₃ by oxy-hydrogen flame. Their properties were investigated by SEM, XRD, TGA-DSC and impedance analyzer. The formed particles in glass soot had spherical shape and the size of approximately 50-100 nm. XRD analysis revealed that the amorphous phase and crystalline phases were mixed in glass soot and the crystalline phases were B(OH)₃ and B₂O₃. The crystalline B(OH)₃ and B₂O₃ found in glass soot completely disappeared by heat treatment. Conductivity was measured by complex impedance method using impedance analyzer and the conductivity was 10⁻⁸ S/cm.     

Dielectric relaxation and conduction mechanism of complex perovskite Ca0.90Sr0.10Cu3Ti3.95Zn0.05O12 ceramic

In this work, Sr and Zn co-doped calcium copper titanate having nominal formula Ca_0.90Sr_0.10Cu₃Ti_3.95Zn_0.05O₁₂ has been synthesized and systematically studied for structure, dielectric and electrical properties. The phase purity of the prepared composition has been confirmed by X-ray diffraction (XRD) pattern and various structural parameters are presented here with Rietveld refinement data. The Scanning electron microscopy (SEM) image revealed the presence of homogeneous fine-grained microstructure investigated in the prepared ceramic. The impedance data well fitted with 2 R-CPE model confirmed the non-ideality of the system. Dielectric studies have shown the existence of two relaxation processes in low and high frequency domains. Low frequency dielectric response proposed as a combination of Maxwell-Wagner relaxation and intrinsic defect (V_o⁺⁺) while high frequency behavior has been interpreted in terms of polaronic relaxation caused by hopping process of an electron between Ti³⁺ and Ti⁴⁺ states. The frequency dependent behavior of conductivity has been well fitted to Dong’s model and interpreted in term of Overlapping Large Polaron Tunneling (OLPT) mechanism. The various parameters; relaxation angular frequency (ω₁) of Debye process, ionic hopping frequency (ω₂₎, dc conductivity (σ_o), cole- cole parameter (α) and frequency exponent (s) have been determined by Dong’s Model fitting.     

Enhancement of density and ionic conductivity for garnet-type Li5La3Ta2O12 solid electrolyte by self-consolidation strategy

Garnet-type Li₅La₃Ta₂O₁₂ (LLTaO) solid electrolyte is a potential candidate component for future all-solid-state batteries due to its extraordinary stability against the reaction with molten lithium. In contrast with traditional cold isostatic pressing (CIP) method, which generally pursues ultra-high pressure, this paper tries to enhance the density and ionic conductivity of LLTaO by self-consolidation strategy without the assistance of any pressing operations. A LLTaO bulk with a relative density of 95% is obtained. SEM images reveal that the bulk sample is assembled by large dense particles in size of tens of microns indicating that the interstitial space among the particles has been dramatically minimized. Accordingly, the total ionic conductivity and the bulk ionic conductivity at 30?°C are promoted up about one order of magnitude higher to 2.63?× 10^?5 S?cm^?1 and 1.41?×?10^?4 S?cm^?1, respectively. Moreover, the lithium ionic migration network in the crystalline unit cell of LLTaO is first explored from its assembled way. A hexagon-like basic unit with tetrahedral Li1 joint sites and Li1- - Li1 edges is identified. The tetrahedral Li1 sites act as crucial junctions for the transportation of lithium ions. This work would significantly stimulate the development of LLTaO electrolyte membrane technology.     

Improvement of the electrochemical properties of novel solid oxide fuel cell anodes, La0.75Sr0.25Cr0.5Mn0.5O3−δ and La4Sr8Ti11Mn0.5Ga0.5O37.5−δ, using Cu-YSZ-based cermets

A Cu-metal-based cermet was used to improve the electrochemical properties of two novel oxide-based systems with intrinsic low electronic conductivity such as La_0.75Sr_0.25Cr_0.5Mn_0.5O_3−δ (LSCM) and La₄Sr₈Ti₁₁Mn_0.5Ga_0.5O_37.5−δ (LSTMG). The introduction of Cu results in a marked improvement of the polarisation resistance values and hence in the performance. The best results correspond to the addition of ∼15% of CuO. In both systems, the polarisation resistances were improved by a least a factor of 2. Despite there are reports claiming that the CuO-zirconia-based systems exhibit catalytic activity, such an improvement seems to be mainly related to the capability of CuO as a sintering agent, helping to bridge electrode particles together, creating new electronic paths and thus effectively increasing the triple phase boundary through the whole electrode material.     

Structural investigation and dielectric studies on Mn substituted Pb(Zr0.65Ti0.35)O3 perovskite ceramics

Polycrystalline samples of manganese substituted lead zirconium titanate (PZMT) with general formula Pb(Zr_0.65−xMn_xTi_0.35)O₃ ceramics have been synthesised by high temperature solid state reaction technique. X-ray diffraction (XRD) patterns were recorded at room temperature to study the crystal structure employing Rietveld technique. All the patterns could be refined to R3c space group with rhombohedral symmetry. Bond lengths and angles have been calculated from refined parameters. Microstructural properties of the materials were analysed by scanning electron microscope (SEM) and compositional analysis were carried out by energy dispersive spectrum (EDS) measurements. All the materials exhibit ferroelectric to paraelectric transition. The Curie temperature (T_c) increases with the Mn concentration. We have observed that dielectric constant decreases and AC conductivity increases with the frequency. The correlation between lattice parameters and T_c for the present samples has been observed.     

Electron-hole transport in (La0.9Sr0.1)0.98Ga0.8Mg0.2O3−δ electrolyte: effects of ceramic microstructure

The oxygen ion transference numbers of a series of (La_0.9Sr_0.1)_0.98Ga_0.8Mg_0.2O_3−δ (LSGM) ceramics with different microstructures, prepared by sintering at 1673 K for 0.5-120 h, were determined at 973-1223 K by a modified Faradaic efficiency technique, taking electrode polarization into account. In air, the transference numbers vary in the range 0.984-0.998, decreasing when temperature or oxygen partial pressure increases. Longer sintering times lead to grain growth and to the dissolution of Sr-rich secondary phases and magnesium oxide, present in trace amounts at the grain boundaries, into the major perovskite phase. This is accompanied with a slight decrease of the total grain-interior resistivity and thermal expansion, while the boundary resistance evaluated from impedance spectroscopy data decreases 3-7 times. The electron-hole transport in LSGM ceramics was found to decrease when the sintering time increases from 0.5 to 40 h, probably indicating a considerable contribution of acceptor-enriched boundaries in the hole conduction. Due to reducing boundary area in single-phase materials, further sintering leads to higher p-type conductivity. The results show that, as for ionic conductivity, electronic transport in solid electrolytes significantly depends on ceramic microstructure.     

Effects of Al2O3 addition on the microstructure and microwave dielectric properties of Ba4Nd9.33Ti18O54 ceramics

Ba₄Nd_9.33Ti₁₈O₅₄·x wt%Al₂O₃ (BNT-A) ceramics (x=0, 0.5, 1.0, 1.5, 2.0, 2.5) were prepared by the conventional solid state reaction. The effects of Al₂O₃ on the microstructure and microwave dielectric properties of Ba₄Nd_9.33Ti₁₈O₅₄ (BNT) ceramics were investigated. X-ray diffraction and backscatter electronic images showed that the Al₂O₃ additive gave rise to a second phase BaAl₂Ti₅O₁₄ (BAT). The formation mechanism and grain growth of the BAT phase were first discussed. Dielectric property test revealed that the Al₂O₃ additive had improved the dielectric properties of the BNT ceramics: increased the Q×f value from 8270 to 12,180 GHz and decreased the τ_f value from 53.4 to 11.2 ppm/°C. A BNT-A ceramic with excellent dielectric properties: ε_r=70.2, Q×f=12,180 GHz, τ_f=20 ppm/°C was obtained with 2.0 wt% Al₂O₃ added after sintering at 1320 °C for 4 h.     

Carbon modified Li2Ti3O7 ramsdellite electrode for Li-ion batteries

An original carbothermal synthesis of ramsdellites phases under specific atmosphere (Ar, Ar/H₂, N₂, N₂/H₂) allowed creating in situ composites which showed good electrochemical properties as negative active materials of Li-ion batteries. The combination of chemical, XRD and electrochemical analyses enabled to identify the as-formed composite electrodes. It consists in ramsdellite/spinel for the synthesis under Ar/H₂, TiO₂ ramsdellite/Li₂TiO₃ for the synthesis under N₂/H₂, and Li_2±xTi₃O₇/Li_2±x′Ti₃O₇ for the samples prepared under both N₂ and Ar. Carbon is partially inserted inside channels of titanate structure for the sample obtained under Ar/H₂. For the first time, one of these composites allowed reaching a specific capacity close to the theoretical value of 198 mAh g⁻¹.     

Thickness dependence of microstructure,dielectric and leakage properties of BaSn0.15Ti0.85O3 thin films

The BaSn_0.15Ti_0.85O₃ (BTS) thin films are prepared on Pt-Si substrates with thickness ranging from ~ 60?nm to ~ 380?nm by radio frequency magnetron sputtering. The effects of thickness on microstructure, surface morphologies and dielectric properties of thin films are investigated. The thickness dependence of dielectric constant is explained based on the series capacitor model that the BTS thin film is consisted by a BTS bulk layer and an interfacial layer (dead layer) between the BTS and bottom electrode. The thin films with thickness of 260?nm give the largest figure of merit of 76.9@100?kHz, while the tunability and leakage current density are 64.6% and 7.46?×?10^?7 A/cm² at 400?kV/cm, respectively.     

Synthesis and characterization of La0.75Sr0.25Cr0.9M0.1O3 perovskites as anodes for CO-fuelled solid oxide fuel cells

A series of La_0.75Sr_0.25Cr_0.9M_0.1O₃ (M = Mn, Fe, Co, Ni) perovskite compounds was synthesized by a modified citrate sol-gel route and employed as anode electrodes on YSZ electrolyte supported SOFC cells. Materials and anode electrodes were characterized for their chemical composition, crystal structure and film morphology. The electrochemical performance of the prepared anodes was evaluated in button cells under SOFC operation with CO/CO₂ mixtures in the temperature range of 900–1000 °C. It was shown that the performance of the perovskite materials in terms of maximum power density follows the sequence Fe > Ni > Co > Mn, based on the substitution cation into the B-site. No carbon deposition was observed under the operating conditions examined, even for prolonged (120 h) exposure to the reaction mixture.     

Relationship between glass network structure and conductivity of Li2O-B2O3-P2O5 solid electrolyte

Solid state glass electrolyte, xLi₂O-(1 − x)(yB₂O₃-(1 − y)P₂O₅) glasses were prepared with wide range of composition, i.e. x = 0.35 - 0.5 and y = 0.17 - 0.67. This material system is one of the parent compositions for chemically and electrochemically stable solid-state electrolyte applicable to thin film battery. Lithium ion conductivity of Li₂O-B₂O₃-P₂O₅ glasses was studied in the correlation to the structural variation of glass network by using FTIR and Raman spectroscopy. The measured ionic conductivity of the electrolyte at room temperature increased with x and y. The maximum conductivity of this glass system was 1.6 × 10⁻⁷ Ω⁻¹ cm⁻¹ for 0.45Li₂O-0.275B₂O₃-0.275P₂O₅ at room temperature. It was shown that the addition of P₂O₅ reduces the tendency of devitrification and increases the maximum amount of Li₂O added into glass former without devitrification. As Li₂O and B₂O₃ contents increased, the conductivity of glass electrolyte increased due to the increase of three-coordinated [BO₃] with a non-bridging oxygen (NBO).     

Lanthanum-doped Bi4Ti3O12 prepared by the soft chemical method: Rietveld analysis and piezoelectric properties

Bi_4−xLa_xTi₃O₁₂ (BLT) thin films and powders with x ranging from 0 to 0.75 were prepared by the polymeric precursor solution. The effect of lanthanum on the structure of BIT powders was investigated by Rietveld Method. The increase of lanthanum content does not lead to any secondary phases. Orthorhombicity of the bismuth titanate (BIT) crystal lattice decreased with the increase of lanthanum content due the reduction of a/b ratio. The BLT films show piezoelectric coefficients of 45, 19, 16 and 10 pm/V for x = 0, 0.25, 0.50 and 0.75, respectively. The piezoelectric response is strongly reduced by the amount of lanthanum added to the system.     

The preparation and characterization of Li4Ti5O12/carbon nano-tubes for lithium ion battery

Li₄Ti₅O₁₂/carbon nano-tubes (CNTs) composite was prepared by sol-gel method while Ti(OC₄H₉)₄, LiCH₃COO·2H₂O and the n-heptane containing CNTs were used as raw materials. The characters of Li₄Ti₅O₁₂/CNTs composite were determined by XRD, SEM, and TG methods. Its electrochemical properties were measured by charge-discharge cycling and impedance tests. It was found that the prepared Li₄Ti₅O₁₂/CNTs presented an excellent rate capability and capacity retention. At the charge-discharge rate of 5C and 10C, its discharge capacities were 145 and 135 mAh g⁻¹, respectively. After 500 cycles at 5C, the discharge capacity retained as 142 mAh g⁻¹. It even could be cycled at the rate of 20C. The excellent electrochemical performance of Li₄Ti₅O₁₂/CNTs electrode could be attributed to the improvement of electronic conductivity by adding conducting CNTs and the nano-size of Li₄Ti₅O₁₂ particles in the Li₄Ti₅O₁₂/CNTs composite.