Synthesis of LiNi1/3Co1/3Mn1/3O2−zFz cathode material from oxalate precursors for lithium ion battery

The layered LiNi_1/3Co_1/3Mn_1/3O_2−zF_z (0 ≤ z ≤ 0.12) cathode materials were synthesized from oxalate precursors by a simple self-propagating solid-state metathesis method with the help of the ball milling and the following calcination. Li(Ac)·2H₂O, Ni(Ac)₂·4H₂O, Co(Ac)₂·4H₂O, Mn(Ac)₂·4H₂O(Ac = acetate), LiF and excess H₂C₂O₄·2H₂O were used as starting materials without any solvent. The structural and electrochemical properties of the prepared LiNi_1/3Co_1/3Mn_1/3O_2−zF_z were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and electrochemical measurements, respectively. The XRD patterns indicate that all samples have a typical hexagonal structure with a space group of . The FESEM images show that the primary particle size of LiNi_1/3Co_1/3Mn_1/3O_2−zF_z gradually increases with increasing fluorine content. Though the fluorine-substituted LiNi_1/3Co_1/3Mn_1/3O_2−zF_z have lower initial discharge capacities, a small amount of fluorine-substituted LiNi_1/3Co_1/3Mn_1/3O_2−zF_z (z = 0.04 and 0.08) exhibit excellent cycling stability and rate capability compared to fluorine-free LiNi_1/3Co_1/3Mn_1/3O₂.     

Structural Characterization of the Complex Perovskites Ba1−xLaxTi1−xCrxO3

The series Ba_1−xLa_xTi_1−xCr_xO₃ (0≤x≤1) was synthesized at 1400°C for about 60 h. Their structure was carefully analyzed by the use of powder X-ray diffraction and Rietveld analysis software GSAS (General Structure Analysis System). Four solid solutions are found in this series: tetragonal solid solution Ba_1−xLa_xTi_1−xCr_xO₃ (0≤x≤0.029), cubic solid solution Ba_1−xLa_xTi_1−xCr_xO₃ (0.0365≤x≤0.600), rhombohedral solid solution Ba_1−xLa_xTi_1−xCr_xO₃ (0.700≤x≤0.873), and orthorhombic solid solution Ba_1−xLa_xTi_1−xCr_xO₃ (0.956≤x≤1). There are corresponding two-phase regions between the adjacent two solid solutions. The detailed lattice parameters are presented. The relationship between the lattice parameters and the composition of the solid solutions is developed.     

Crystal structure, thermal expansion and conductivity of anisotropic La1−xSrxGa1−2xMg2xO3−y (x=0.05, 0.1) single crystals

Crystal structure and anisotropy of the thermal expansion of single crystals of La_1−xSr_xGa_1−2xMg_2xO_3−y (x=0.05 and 0.1) were measured in the temperature range 300-1270 K. High-resolution X-ray powder diffraction data obtained by synchrotron experiments have been used to determine the crystal structure and thermal expansion. The room temperature structure of the crystal with x=0.05 was found to be orthorhombic (Imma, Z=4, a=7.79423(3) Å, b=5.49896(2) Å, c=5.53806(2) Å), whereas the symmetry of the x=0.1 crystal is monoclinic (I2/a, Z=4, a=7.82129(5) Å, b=5.54361(3) Å, c=5.51654(4) Å, β=90.040(1)°). The conductivity in two orthogonal directions of the crystals has been studied. Both, the conductivity and the structural data indicate three phase transitions in La_0.95Sr_0.05Ga_0.9Mg_0.1O_2.92 at 520-570 K (Imma-I2/a), 770 K (I2/a-R3c) and at 870 K (R3c-R-3c), respectively. Two transitions at 770 K (I2/a-R3c) and in the range 870-970 K (R3c-R-3c) occur in La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85.     

Crystal structure, microstructure and reducibility of LaNixCo1−xO3 and LaFexCo1−xO3 Perovskites (0<x≤0.5)

Nickel and iron substituted LaCoO₃ with rhombohedrally distorted perovskite structure were obtained in the temperature range of 600-900 °C by thermal decomposition of freeze-dried citrates and by the Pechini method. The crystal structure, morphology and defective structure of LaCo_1−xNi_xO₃ and LaCo_1−xFe_xO₃ were characterized by X-ray diffraction and neutron powder diffraction, TEM and SEM analyses and electron paramagnetic resonance spectroscopy. The reducibility was tested by temperature programmed reduction with hydrogen. The products of the partial and complete reduction were determined by ex-situ XRD experiments. The replacement of Co by Ni and Fe led to lattice expansion of the perovskite structure. For perovskites annealed at 900 °C, there was a random Ni, Fe and Co distribution. The morphology of the perovskites does not depend on the Ni and Fe content, nor does it depend on the type of the precursor used. LaCo_1−xNi_xO₃ perovskites (x>0.1) annealed at 900 °C are reduced to Co/Ni transition metal and La₂O₃ via the formation of oxygen deficient Brownmillerite-type compositions. For LaCo_1−xNi_xO₃ annealed at 600 °C, Co/Ni metal, in addition to oxygen-deficient perovskites, was formed as an intermediate product at the initial stage of the reduction. The interaction of LaCo_1−xFe_xO₃ with H₂ occurs by reduction of Co³⁺ to Co²⁺ prior to the Fe³⁺ ions. The reducibility of Fe-substituted perovskites is less sensitive towards the synthesis procedure in comparison with that of Ni substituted perovskites.     

Thermoelectric properties of polycrystalline La1−xSrxCoO3

Thermoelectric properties of polycrystalline La_1−xSr_xCoO₃, where Sr²⁺ is substituted in La³⁺ site in perovskite-type LaCoO₃, have been investigated. Sr-doping increases the electrical conductivity (σ) of La_1−xSr_xCoO₃, and also decreases the Seebeck coefficient (S) for 0.01?x?0.40. A Hall coefficient measurement reveals that the increase in electrical conductivity arises from increases in both carrier concentration and the Hall mobility. The decrease in the Seebeck coefficient is caused by a decrease in carrier effective mass as well as increase in carrier concentration. The highest power factor (σS²) is 3.7×10⁻⁴ W m⁻¹ K⁻² at 250 K for x=0.10. The thermal conductivity (κ) is about 2 W m⁻¹ K⁻¹ at 300 K for 0?x?0.04, and increases for x?0.05 because of an increase in heat transport by conductive carrier. The thermoelectric properties of La_1−xSr_xCoO₃ are improved by Sr-doping, and the figure of merit (Z=σS² κ⁻¹) reaches 1.6×10⁻⁴ K⁻¹ for x=0.06 at 300 K (ZT=0.048). For heavily Sr-doped samples, the thermoelectric properties diminish mainly because of the decrease in the Seebeck coefficient and the increase in thermal conductivity.     

Structural and dielectric/ferroelectric properties of (La1−xNdx)2Ti2O7 synthesized by sol-gel route

A series of compounds with the general formula (La_1−xNd_x)₂Ti₂O₇ (0.0≤x≤1.0) has been prepared by the sol-gel method. The decomposition of the gel was characterized by thermo-gravimetric analysis coupled to mass spectrometry, indicating the reaction is achieved above 850 °C. The lattice parameters versus x show an expected decrease in the a and b parameters while c and the β angle remain almost unchanged with respect to the monoclinic symmetry conserved for the full solid solution. Dielectric, piezoelectric and ferroelectric properties were measured on the entire series.     

XANES Study on the Generation and Distribution of Holes via Ca Substitution and O Doping in Cu(Ba0.8Sr0.2)2(Yb1−xCax)Cu2O6+z

Generation of holes is facilitated in the Cu(Ba_0.8Sr_0.2)₂ (Yb_1−xCa_x)Cu₂O_6+z (Cu-1212) system by two independent ways, i.e., by Ca substitution (0≤x≤0.35) and O doping (0<z<1). The distribution of holes between the CuO₂-(Yb_1−xCa_x)-CuO₂ block containing two identical superconductive CuO₂ planes and the “charge-reservoir” block consisting of a single CuO_z chain has been quantitatively investigated by means of O K-edge and Cu L_2,3-edge X-ray absorption near-edge structure (XANES) spectroscopy. The resultant values for the CuO₂-plane hole concentration are compared with those calculated employing the bond-valence-sum (BVS) method from the neutron powder diffraction (NPD) data previously reported for the same samples. The results of the two methods are in good agreement. The two independent hole-doping ways are found to result in different distributions of holes over the crystal, i.e., different ratios of hole numbers at the CuO₂ plane and the CuO_z chain. With Ca substitution holes are directed efficiently into the CuO₂ plane, while for O doping holes are more homogeneously distributed between the CuO₂ plane and the CuO_z chain. Moreover, the value of T_c at a fixed CuO₂-plane hole concentration is shown to be higher for Ca-substituted than for O-doped samples.     

Temperature and composition dependent structural investigation of the defect perovskite series Sr1−xTi1−2xNb2xO3, 0≤x≤0.2

The crystal structure of the defect perovskite series Sr_1−xTi_1−2xNb_2xO₃ has been investigated over a range of temperatures using high-resolution synchrotron X-ray diffraction, neutron diffraction and electron diffraction. Three distinct regions were observed: 0<x≤0.125 was a solid solution of Sr_1−xTi_1−2xNb_2xO₃ with minor SrTiO₃ intergrowth, 0.125<x≤0.2 was a pure Sr_1−xTi_1−2xNb_2xO₃ solid solution adopting the cubic perovskite type structure (Pm3¯m) and for x>0.2 Sr_0.8Ti_0.6Nb_0.4O₃ and Sr₃TiNb₄O₁₅ formed a two phase region. The cubic structure for Sr_0.8Ti_0.6Nb_0.4O₃ was stable over the temperature range 90-1248 K and the thermal expansion co-efficient was determined to be 8.72(9)×10⁻⁶ K⁻¹. Electron diffraction studies revealed diffuse scattering due to local scale Ti/Nb displacements and slightly enhanced octahedral rotations that did not lead to long range order. The octahedral rotations were observed to ‘lock-in’ at temperatures below ∼75 K resulting in a tetragonal structure (I4/mcm) with anti-phase octahedral tilting about the c-axis.     

Synthesis and electrical conductivity of perovskite-type PrCo1−xMgxO3

Oxides in the system PrCo_1−xMg_xO₃ (x=0.0, 0.05, 0.10, 0.15, 0.20, 0.25) were synthesized by citrate technique and characterized by powder X-ray diffraction and scanning electron microscope. All compounds have a cubic perovskite structure (space group ). The maximum ratio of doped Mg in the system PrCo_1−xMg_xO₃ is x=0.2. Further doping leads to the segregation of Pr₆O₁₁ in PrCo_1−xMg_xO₃. The substitution of Mg for Co improves the performance of PrCoO₃ as compared to the electrical conductivity measured by a four-probe electrical conductivity analyzer in the temperature range from 298 to 1073 K. The substitution of Mg for Co on the B site may be compensated by the formations of Co⁴⁺ and oxygen vacancies. The electrical conductivity of PrCo_1−xMg_xO₃ oxides increases with increasing x in the range of 0.0-0.2. The increase in conductivity becomes considerable at the temperatures ?673 K especially for x?0.1; it reaches a maximum at x=0.2 and 1073 K. From x>0.2 the conductivity of PrCo_1−xMg_xO₃ starts getting lower. This is probably a result of the segregation of Pr₆O₁₁ in PrCo_1−xMg_xO₃ , which blocks oxygen transport, and association of oxygen vacancies. A change in activation energy for all PrCo_1−xMg_xO₃ compounds (x=0-0.25) was observed, with a higher activation energy above 573 K and a lower activation energy below 573 K. The reasons for such a change are probably due to the change of dominant charge carriers from Co⁴⁺ to Vö in PrCo_1−xMg_xO₃ oxides and a phase transition mainly starting at 573 K.     

Crystal structure and electrical conductivity of lanthanum-calcium chromites-titanates La1−xCaxCr1−yTiyO3−δ (x=0-1, y=0-1)

Five series of perovskite-type compounds in the system La_1−xCa_xCr_1−yTi_yO₃ with the nominal compositions y=0, x=0-0.5; y=0.2, x=0.2-0.8; y=0.5, x=0.5-1.0; y=0.8, x=0.6-1.0 and y=1, x=0.8-1 were synthesized by a ceramic technique in air (final heating 1350 °C). On the basis of the X-ray analysis of the samples with (Ca/Ti)?1, the phase diagram of the CaTiO₃-LaCr^IIIO₃-CaCr^IVO₃ quasi-ternary system was constructed. Extended solid solution with a wide homogeneity range is formed in the quasi-ternary system CaCr^IVO₃-CaTiO₃-LaCr^IIIO₃. The solid solution La_{(1−x′−y)}Ca_(x′+y)Cr^IV_x′Cr^III_{(1−x′−y)}Ti_yO₃ exists by up to 0.6-0.7 mol fractions of CaCr^IVO₃ (x^′<0.6-0.7) at the experimental conditions. The crystal structure of the compounds is orthorhombic in the space group Pbnm at room temperature. The lattice parameters and the average interatomic distances of the samples within the solid solution ranges decrease uniformly with increasing Ca content. Outside the quasi-ternary system, the nominal compositions La_0.1Ca_0.9TiO₃, La_0.2Ca_0.8TiO₃, La_0.4Ca_0.6Cr_0.2Ti_0.8O₃ and La_0.3Ca_0.7Cr_0.2Ti_0.8O₃ in the system La_1−xCa_xCr_1−yTi_yO₃ were found as single phases with an orthorhombic structure. In the temperature range between 850 and 1000 °C, the synthesized single-phase compositions are stable at pO₂=6×10⁻¹⁶-0.21×10⁵ Pa. Oxygen stoichiometry and electrical conductivity of the separate compounds were investigated as functions of temperature and oxygen partial pressure. The chemical stability of these oxides with respect to oxygen release during thermal dissociation decreases with increasing Ca-content. At 900 °C and oxygen partial pressure 1×10⁻¹⁵-0.21×10⁵ Pa, the compounds with x>y (acceptor doped) are p-type semiconductors and those with x<y (donor doped) and x=y are n-type semiconductors. The type and level of electrical conductivity are functions of the concentration ratios of cations occupying the B-sites of the perovskite structures: [Cr³⁺]/[Cr⁴⁺] and [Ti⁴⁺]/[Ti³⁺]. The maximum electrical conductivity at 900 °C and pO₂=10⁻¹⁵ Pa was found for the composition La_0.1Ca_0.9TiO₃ (near 50 S/cm) and in air at 900 °C for La_0.5Ca_0.5CrO₃ (close to 100 S/cm).     

Enzyme mimics of spinel-type CoxNi1−xFe2O4 magnetic nanomaterial for eletroctrocatalytic oxidation of hydrogen peroxide

A series of spinel-type Co_xNi_1−xFe₂O₄ (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) magnetic nanomaterials were solvothermally synthesized as enzyme mimics for the eletroctrocatalytic oxidation of H₂O₂. X-ray diffraction and scanning electron microscope were employed to characterize the composition, structure and morphology of the material. The electrochemical properties of spinel-type Co_xNi_1−xFe₂O₄ with different (Co/Ni) molar ratio toward H₂O₂ oxidation were investigated, and the results demonstrated that Co_0.5Ni_0.5Fe₂O₄ modified carbon paste electrode (Co_0.5Ni_0.5Fe₂O₄/CPE) possessed the best electrocatalytic activity for H₂O₂ oxidation. Under optimum conditions, the calibration curve for H₂O₂ determination on Co_0.5Ni_0.5Fe₂O₄/CPE was linear in a wide range of 1.0 × 10⁻⁸–1.0 × 10⁻³ M with low detection limit of 3.0 × 10⁻⁹ M (S/N = 3). The proposed Co_0.5Ni_0.5Fe₂O₄/CPE was also applied to the determination of H₂O₂ in commercial toothpastes with satisfactory results, indicating that Co_xNi_1−xFe₂O₄ is a promising hydrogen peroxidase mimics for the detection of H₂O₂.     

Formation, sintering, and electrical conductivity of perovskite Sm(Cr1−xMgx)O3 (0?x?0.23) prepared by the hydrazine method

The presence of SmCrO₄ is experimentally established. In Mg²⁺-substituted SmCrO₃, single-phase perovskite Sm(Cr_1−xMg_x)O₃, where x=0-0.23, are formed at ∼830°C by decomposition of Sm(Cr_1−xMg_x)O₄ which crystallizes at 530-570°C from amorphous materials prepared by the hydrazine method. Sm(Cr_1−xMg_x)O₃ solid solution powders consisting of submicrometer-size particles are sinterable; dense materials can be fabricated by sintering for 2 h at 1700°C in air. The relative densities, grain sizes, and electrical conductivities increase with increased Mg²⁺ content. Sm(Cr_0.77Mg_0.23)O₃ materials exhibit an excellent direct current electrical conductivity of 2.2×10³ S m⁻¹ at 1000°C.     

Structural, magnetic, and electrochemical studies on lithium insertion materials LiNi1−xCoxO2 with 0≤x≤0.25

The structural, magnetic, and electrochemical properties of the LiNi_1−xCo_xO₂ samples with x= 0, 0.05, 0.1, and 0.25 have been investigated by powder X-ray diffraction analyses, magnetic susceptibility (χ) measurements, and electrochemical charge and discharge test in non-aqueous lithium cell. According to the structural analyses using a Rietveld method, the occupancy of the Ni ions in the Li layer was estimated to be below 0.01 for all the samples and was eventually independent of x. The temperature (T) dependence of χ⁻¹ obtained with the magnetic field H=10 kOe indicated that all the samples are a Curie-Weiss paramagnet down to . At low T, all the samples entered into a spin-glass-like phase below T_f. The magnitude of T_f was found to decrease almost linearly with x, as in the case for the x dependences of the lattice parameters of a_h- and c_h-axes, Weiss temperature, and effective magnetic moment. It is, therefore, found that the change of the magnetic properties with x is simply explained by a dilution effect due to the increase of the quantity of Co³⁺ ions. On the other hand, the electrochemical measurements demonstrated that the irreversible capacity at the initial cycle is drastically decreased by the small amount of Co ions. Furthermore, the discharge capacity (Q_dis) for the x=0.05 and 0.1 samples are larger than that for the x=0 sample; namely, Q_dis=180 mAh g⁻¹ for x=0, Q_dis=217 mAh g⁻¹ for x=0.05, and Q_dis=206 mAh g⁻¹ for x=0.1. Comparing with the past results, the amount of Ni ions in the Li layer is found to play a significant role for determining the magnetic and electrochemical properties of LiNi_1−xCo_xO₂.     

Chemical Synthesis and Properties of Spinel Li1−xCo2O4−δ

Spinel Li_1−xCo₂O_4−δ samples with 0.44≤(1−x)≤1 have been synthesized by chemically extracting lithium with the oxidizer NO₂BF₄ in acetonitrile medium from the LT-LiCoO₂ synthesized at 400°C. Rietveld analysis of the X-ray diffraction data reveals that the Li_1−xCo₂O_4−δ samples adopt the normal cubic spinel structure with a cation distribution of (Li_1−x)_8a[Co₂]_16dO_4−δ. Redox iodometric titration data indicate that the LT-LiCoO₂ tends to lose oxygen on extracting lithium and the spinel Li_1−xCo₂O_4−δ samples are oxygen-deficient. Both infrared spectroscopic and magnetic susceptibility data suggest that the LiCo₂O_4−δ spinel is metallic with itinerant electrons. The tendency to lose oxygen on extracting lithium from the LT-LiCoO₂ and the observed metallic behavior of the spinel LiCo₂O_4−δ are explained on the basis of a qualitative band diagram.     

Effects of vacancy concentration on the magnetic and transport properties of (La1−xPbx)1−y□yMnO3

(La_1−xPb_x)_1−y□_yMnO₃ with x=0.05-0.5 and y=0, 0.05, 0.1 (where □ is a vacancy) was studied to evaluate the effects of A-site vacancies on the physical properties. In this system manganese perovskites form with tolerance factors close to 1 and low A-site cation size mismatch due to similarities in the effective ionic radii of La³⁺ and Pb²⁺. Increasing vacancy concentration indicates no significant effect on the lattice parameters or volume. However, the vacancies introduce a greater A-site cation size mismatch, which leads to a lowering of the ferromagnetic and metal-insulator transition temperatures, although the transitions are not broadened with increasing vacancy content. Due to the vacancies a distribution of Mn-O-Mn angles and Mn-O distances are created, and long range order in (La_1−xPb_x)_1−y□_yMnO₃ appears to be determined by Mn-O-Mn angles and Mn-O distances which most distort from 180° and are the longest, respectively, in the structure.     

Perovskite-type SrTi1−xNbx(O,N)3 compounds: Synthesis, crystal structure and optical properties

The synthesis, crystal structure, thermal stability and absorbance spectra of perovskite-type oxynitrides with the general formula SrTi_1−xNb_x(O,N)₃ (x=0.05, 0.10, 0.20, 0.50, 0.80, 0.90, 0.95) have been investigated. Oxide samples were prepared by a polymerized complex synthesis route and post-treated under ammonia at 850 °C for 24 h to substitute nitrogen for oxygen. Synchrotron X-ray powder diffraction (XRD) evidenced that the mixed oxide phases were all transformed into oxynitrides with perovskite-type structure during a thermal ammonolysis. SrTi_1−xNb_x(O,N)₃ with compositions x≤0.80 crystallized in a cubic and samples with x≥0.90 in a tetragonal structure. The Rietveld refinement indicated a continuous enlargement of the lattice parameters towards higher niobium content of the samples. Thermogravimetric analysis (TGA) and hotgas extraction revealed the dependence of the nitrogen incorporation upon the degree of niobium substitution. It showed that more nitrogen was detected in the samples with higher niobium content. Furthermore, TGA disclosed stability for all oxynitrides at T≤400 °C. Diffuse reflectance spectroscopy indicated a continuous decrease of the band gap’s width from 3.24 eV (SrTi_0.95Nb_0.05 (O,N)₃) to 1.82 eV (SrTi_0.05Nb_0.95(O,N)₃) caused by the increasing amount of nitrogen towards the latter composition.     

Comparison of the Chemical Stability of Li1−xCoO2 and Li1−xNi0.85Co0.15O2 Cathodes

The chemical stability of the layered Li_1−xCoO₂ and Li_1−xNi_0.85Co_O.15O₂ cathodes is compared by monitoring the oxygen content with lithium content (1−x) in chemically delithiated samples. The Li_1−xCoO₂ system tends to lose oxygen from the lattice at deep lithium extraction while the Li_1−xNi_0.85Co_0.15O₂ system does not lose oxygen at least for (1−x)>0.3. This difference seems to result in a lower reversible (practical) capacity (140 mA h/g) for LiCoO₂ compared to that for LiNi_0.85Co_0.15O₂ (180 Ma h/g). The loss of significant amount of oxygen leads to a sliding of oxide layers and the formation of a major P3 and a minor O1 phase for the end member CoO_2−δ with δ=0.33. In contrast, Ni_0.85Co_0.15O_2−δ with a small amount of δ=0.1 maintains the initial O3 layer structure.     

Magnetostructural correlations in the antiferromagnetic Co2−x Cux(OH)AsO4 (x=0 and 0.3) phases

The Co_2−xCu_x(OH)AsO₄ (x=0 and 0.3) compounds have been synthesized under mild hydrothermal conditions and characterized by X-ray single-crystal diffraction and spectroscopic data. The hydroxi-arsenate phases crystallize in the Pnnm orthorhombic space group with Z=4 and the unit-cell parameters are a=8.277(2) Å, b=8.559(2) Å, c=6.039(1) Å and a=8.316(1) Å, b=8.523(2) Å, c=6.047(1) Å for x=0 and 0.3, respectively. The crystal structure consists of a three-dimensional framework in which M(1)O₅-trigonal bipyramid dimers and M(2)O₆-octahedral chains (M=Co and Cu) are present. Co₂(OH)AsO₄ shows an anomalous three-dimensional antiferromagnetic ordering influenced by the magnetic field below 21 K within the presence of a ferromagnetic component below the ordering temperature. When Co²⁺ is partially substituted by Cu²⁺ions, Co_1.7Cu_0.3(OH)AsO₄, the ferromagnetic component observed in Co₂(OH)AsO₄ disappears and the antiferromagnetic order is maintained in the entire temperature range. Heat capacity measurements show an unusual magnetic field dependence of the antiferromagnetic transitions. This λ-type anomaly associated to the three-dimensional antiferromagnetic ordering grows with the magnetic field and becomes better defined as observed in the non-substituted phase. These results are attributed to the presence of the unpaired electron in the dx²−y² orbital and the absence of overlap between neighbour ions.     

Luminescent and structural properties of the series Ba6−xEuxTi2+xTa8−xO30 and Ba4−yKyEu2Ti4−yTa6+yO30

The series Ba_6−xEu_xTi_2+xTa_8−xO₃₀ and Ba_4−yK_yEu₂Ti_4−yTa_6+yO₃₀ have been synthesized at 1400°C in air. They exhibit efficient excitation at about 400 nm and typical emission of Eu³⁺ at about 580-620 nm, form solid solutions within 0.0?x?2.0 and 0?y?4 respectively, and crystallized in P4/mbm at room temperature with Eu atoms occupied at centrosymmetric site (0, 0, 0). Their conductivity is very low (2.8×10⁻⁶ Ω⁻¹ cm⁻¹ at 740°C for Ba₆Ti₂Ta₈O₃₀).