Preparation,phase structure and microwave dielectric properties of CoLi2/3Ti4/3O4 ceramic

A new low loss microwave dielectric ceramic with composition of CoLi_2/3Ti_4/3O₄ was prepared by a conventional solid-state reaction method. The compound has a cubic spinel structure [Fd-3m (227)] similar to MgFe₂O₄ with lattice parameters of a = 8.3939 Å, V = 591.42 Å³, Z = 8 and ρ = 4.30 g/cm³. This ceramic has a low sintering temperature (～1050 °C) and good microwave dielectric properties with relative permittivity of 21.4, Q × f value of 35,000 GHz and τ_f value of ?22 ppm/°C. Furthermore, the addition of BaCu(B₂O₅) (BCB) can effectively lower the sintering temperature from 1050 °C to 900 °C and does not induce much degradation of the microwave dielectric properties. Compatibility with Ag electrode indicates that the BCB added CoLi_2/3Ti_4/3O₄ ceramics are good candidates for LTCC applications.     

Influence of CuO addition to BaSm2Ti4O12 microwave ceramics on sintering behavior and dielectric properties

Microwave dielectric ceramics of tungsten–bronze-type BaSm₂Ti₄O₁₂ were prepared by doping CuO (up to 2 wt.%) as the liquid-phase sintering aid. The effects of CuO additive on the densification, micro structure and dielectric properties were investigated. Due to the liquid-phase effect, the sintering temperature of BaSm₂Ti₄O₁₂ ceramics with 1 wt.% CuO addition can be effectively reduced to 1160 °C, about 200 °C lower than that of pure BaSm₂Ti₄O₁₂ ceramics, while good microwave dielectric properties of ɛ_r = 75.8, Q*f = 4914.6 GHz and τ_f = −7.65 ppm/°C were still achieved.     

Preparation,characterization and dielectric properties of Ba5LnZnTa9O30 (Ln=La,Sm) ceramics

Ba₅LnZnTa₉O₃₀ (Ln=La, Sm) ceramics were prepared by high temperature solid-state reaction route. The samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) methods. They belong to paraelectric phase of filled tetragonal TB structure at room temperature with unit cell a=12.5909(4) Å, c=3.9622(2) Å for Ba₅LaZnTa₉O₃₀; and a=12.5777(4) Å, c=3.9544(2) Å for Ba₅SmZnTa₉O₃₀. At 1 MHz, Ba₅LaZnTa₉O₃₀ has high dielectric constants of 89 with low dielectric loss 0.0067, and temperature coefficients of the dielectric constant (τ_ε) −811 ppm °C⁻¹; Ba₅LaZnTa₉O₃₀ has dielectric constants of 74 with low dielectric loss 0.0035, and τ_ε −474 ppm °C⁻¹.     

Optical constants and crystal chemical parameters of Sc2W3O12

The refractive indices of Sc₂W₃O₁₂, measured at wavelengths of 435.8–643.8 nm, were used to calculate n_a = 1.7331, n_b = 1.7510, n_c = 1.7586 at λ = 589.3 nm and n_∞ values at λ = ∞ from a one-term Sellmeier equation. Mean refractive indices, 〈n_D〉, and mean dispersion values, 〈A〉, are, respectively, 1.7475 and 110 × 10^?16 m². Total electronic polarizabilities, α_obs, were calculated from n_∞ and the Lorenz–Lorentz equation. The unusually large difference between the observed polarizability of 28.415 Å³ and the calculated total polarizability α_T of 26.74 Å³ (Δ = +6.3%) is attributed to (1) a large M–O–W angle, and (2) a high degree of W 5d–O 2p and Sc nd–O 2p hybridization, where n signifies unspecified Sc d orbitals.     

Hydrothermal synthesis,crystal structure and characterization of LiCoP5O14·H2O: A new condensed layered penta phosphate crystals

A new family of condensed hydrated lithium cobalt penta phosphate (LiCoP₅O₁₄·H₂O) crystals were synthesized by hydrothermal technique and characterized by X-ray diffraction method. The compound crystallizes in monoclinic system with space group P21/c and cell parameters a = 10.788(4) Å, b = 9.761(3) Å, c = 9.788(5) Å, β = 101.249(1) Å, Z = 4, exhibiting layer type polymeric structure. DTA study indicates that this compound has low thermal stability and magnetically frequency dependent paramagnetic behaviour.     

Synthesis,crystal structure refinement,electrical and magnetic properties of BaV13O18 and SrV13O18

Polycrystalline samples of BaV₁₃O₁₈ and SrV₁₃O₁₈ were prepared by solid-state reaction of BaCO₃, SrCO₃, V₂O₅ and V at 1773–2073 K in flowing Ar. The crystal structures of BaV₁₃O₁₈ (R-3, a_h=12.6293(10) Å, c_h=7.0121(4) Å) and SrV₁₃O₁₈ (a_h=12.5491(7) Å, c_h=6.9878(3) Å) were refined by the Rietveld method using X-ray diffraction data. BaV₁₃O₁₈ exhibited semiconducting behavior with electrical resistivity from 5.8×10⁻³ to 2.7×10⁻³ Ω cm at 100–300 K. Electrical resistivity of SrV₁₃O₁₈ ranged from 1.5×10⁻³ to 1.8×10⁻³ Ω cm, and it increased slightly up to around 250 K and decreased above 250 K with increasing temperature. Negative Seebeck coefficients of both compounds at 100–300 K indicated that electron was the dominant carrier. BaV₁₃O₁₈ and SrV₁₃O₁₈ showed paramagnetism with the effective magnetic moment of 0.11μ_B and 0.15μ_B, respectively, at 10–100 K.     

High-pressure synthesis and magnetic properties of complex oxide Y2Cd2/3Re4/3O7

A new complex oxide Y₂Cd_2/3Re_4/3O₇ with hexagonal cell parameters a = 7.3564(2) Å, c = 17.7092(5) Å (space group P3₁21, z = 6, zirkelite structure type) was synthesized from Y₃ReO₈, ReO₂, metallic Re and CdO under pressure 6 GPa and temperature 1500 °C. Magnetic susceptibility measured in the temperature range from 2 to 300 K depends little on temperature above ∼50 K and is indicative of a delocalized or intermediate character of d electrons of Re⁵⁺ cations.     

Effect of V2O5 additive to 0.4SrTiO3–0.6La(Mg0.5Ti0.5)O3 ceramics on sintering behavior and microwave dielectric properties

The effect of V₂O₅ addition on the microwave dielectric properties and the microstructures of 0.4SrTiO₃–0.6La(Mg_0.5Ti_0.5)O₃ ceramics sintered for 5 h at different sintering temperature were investigated systematically. It was found that the sintering temperature was effectively lowered about 200 °C by increasing V₂O₅ addition content. The grain sizes, bulk density as well as microwave dielectric properties were greatly dependent on sintering temperature and V₂O₅ content. The 4ST–6LMT ceramics with 0.25% V₂O₅ sintered at 1400 °C for 5 h in air exhibited optimum microwave dielectric properties of ɛ_r = 50.7, Q × f = 15049.6 GHz, T_f = −1.7 ppm/°C.     

Synthesis and structure determination of new open-framework chromium carboxylate MIL-105 or CrIII(OH)·{O2C–C6(CH3)4–CO2}·nH2O

Two new three-dimensional chromium(III) dicarboxylate, MIL-105 or Cr^III(OH)·{O₂C-C₆(CH₃)₄-CO₂}·nH₂O, have been obtained under hydrothermal conditions, and their structures solved using X-ray powder diffraction data. Both solids are structural analogs of the known Cr benzenedicarboxylate compound (MIL-53). Both contain trans corner-sharing CrO₄(OH)₂ octahedral chains connected by tetramethylterephthalate di-anions. Each chain is linked by the ligands to four other chains to form a three-dimensional framework with an array of 1D pores channels. The pores of the high temperature form of the solid, MIL-105ht, are empty. However, MIL-105ht re-hydrates at room temperature to finally give MIL-105lt with pores channels filled with free water molecules (lt: low temperature form; ht: high temperature form). The thermal behaviour of the two solids has been investigated using TGA. Crystal data for MIL-105ht: monoclinic space group C2/c with a = 19.653(1) Å, b = 9.984(1) Å, c = 6.970(1) Å, β = 110.67(1)° and Z = 4. Crystal data for MIL-105lt: orthorhombic space group Pnam with a = 17.892(1) Å, b = 11.165(1) Å, c = 6.916(1) Å and Z = 4.     

Microwave dielectric properties of Ba(Mg1/3Ta(2−2x)/3Wx/3Tix/3)O3 ceramics

The microwave dielectric properties of ceramics based on Ba(Mg_1/3Ta_(2−2x)/3W_x/3Ti_x/3)O₃ is investigated as a function of x. The densification as well as dielectric properties deteriorate with increase in the substitution levels of (Ti_1/3W_1/3)^3.33+ at (Ta_2/3)^3.33+ site in Ba(Mg_1/3Ta_2/3)O₃. The τ_f is approaching zero between x = 0.1 and 0.15 in Ba(Mg_1/3Ta_(2−2x)/3W_x/3Ti_x/3)O₃ where quality factor is reasonably good (Q_u × f = 80,000–90,000 GHz). The Ba(Mg_1/3Ta_(2−2x)/3W_x/3Ti_x/3)O₃ with x = 1.0 has ɛ_r = 15.4, τ_f = −25.1 ppm/°C, Q_u × f = 35,400 GHz.     

Low-temperature sintering and microwave dielectric properties of CaTi1−x(Fe0.5Nb0.5)xO3 ceramics with B2O3 addition

CaTi_1−x(Fe_0.5Nb_0.5)_xO₃ (0 ≤ x ≤ 1) dielectrics were synthesized via the solid state reaction route and structure analysis was performed together with the dielectric characterization. The substitution of Ti⁴⁺ by Fe³⁺/Nb⁵⁺ and developed phase were studied by X-ray diffraction. The dielectric constant and temperature coefficient of resonant frequency decrease rapidly with an increase of x. The influence of 1–5 wt.% B₂O₃ as a sintering additive investigated at CaTi_0.5(Fe_0.5Nb_0.5)_0.5O₃ solid solutions. The dielectric properties were found to strongly depend on the sintering conditions and contents of B₂O₃ additions. ɛ_r = 52.3, Q × f_o = 2930 GHz and T_f = 13 ppm/°C were obtained for CaTi_0.5(Fe_0.5Nb_0.5)_0.5O₃ specimen 3 wt.% B₂O₃ sintered at 900 °C for 2 h.     

Microwave dielectric properties of BaO–TeO2 binary compounds

A series of BaO–TeO₂ binary ceramic compounds were explored for microwave dielectric applications with ultra-low processing temperatures. During the calcination of mixed BaCO₃ and TeO₂ raw powders, BaTe₄O₉, BaTe₂O₆, BaTeO₃, and Ba₂TeO₅ phases were obtained through the sequential phase formations from Te-rich to Ba-rich phases at temperatures ranging from 500 to 850 °C. Sintering temperatures were as low as only 550 °C for the Te-rich phases. Barium tellurate ceramics exhibited excellent microwave dielectric properties with intermediate dielectric permittivities and high quality factors (Q). The dielectric properties at microwave frequencies were ε_r = 10–21, Q × f = 34,000–55,000 GHz, and TCf = − 51 to − 124 ppm/°C, depending on compositions.     

Fluorine intercalation in the n = 1 and n = 2 layered manganites Sr2MnO3.5+x and Sr3Mn2O6

Fluorine insertion into the oxygen defect superstructure manganite Sr₂MnO_3.5+x has been shown by transmission electron microscopy (TEM) to result in two levels of fluorination. In the higher fluorine content sections, the fluorine anions displace oxygen anions from their apical positions into the equatorial vacancies, thus destroying the superstructure and reverting to a K₂NiF₄-type structure (a = 3.8210(1) Å and c = 12.686(1) Å). Conversely, lower fluorine content sections retain the Sr₂MnO_3.5+x defect superstructure, crystallising in the P2₁/c space group. Fluorine intercalation into the reduced double-layer manganite Sr₃Mn₂O₆ occurs in a step-wise fashion according to the general formula Sr₃Mn₂O₆F_y with y = 1, 2, and 3. It is proposed that the y = 1 phase (a = 3.815(1) Å, c = 20.29(2) Å) is produced by the filling of all the equatorial oxygen vacancies by fluorine atoms whilst the y = 2 phase (a = 3.8222(2) Å, c = 21.2435(3) Å) has a random distribution of fluorine anions throughout both interstitial rocksalt and equatorial sites. Neutron powder diffraction data suggest that the fully fluorinated y = 3 phase (a = 3.8157(6) Å, c = 23.666(4) Å) corresponds to the complete occupation of all the equatorial oxygen vacancies and the interstitial sites by intercalated fluorine.     

Microwave dielectric characteristics of Mg(Ta1−xNbx)2O6 ceramics

The crystalline phase and the microwave dielectric properties of the Mg(Ta_1−xNb_x)₂O₆ ceramics have been investigated. Combining the positive temperature coefficient of the resonant frequency (τ_f) material (MgTa₂O₆, τ_f = +30 ppm/°C) with the negative one (MgNb₂O₆, τ_f = −70 ppm/°C) can produce the composite with τ_f ∼ 0 ppm/°C. The crystal structure of pure MgTa₂O₆ ceramic is the tetragonal structure. For x = 0.15, the crystal structure of the solid solution was the coexistence of the tetragonal structure and orthorhombic structure. Solid solutions with 0.25 ≦ x ≦ 1 exhibit the orthorhombic structure, which is like the structure of pure MgNb₂O₆ ceramic. The sintered morphologies of Mg(Ta_1−xNb_x)₂O₆ ceramics gradually change from the disk-typed grains (x = 0 and 0.15) to the disk-typed and bar-typed grains coexist (x = 0.35, 0.5, and 0.7), and then reveal the bar-typed grains (x = 0.85 and 1). The densities, dielectric constants (ɛ_r) and τ_f values of Mg(Ta_1−xNb_x)₂O₆ ceramics decrease with the increase of the MgNb₂O₆ content. The quality factor (Q × f) reaches the minimum value at x = 0.15, and then increases with the increase of the MgNb₂O₆ content. The Mg(Ta_1−xNb_x)₂O₆ ceramic with x = 0.25 sintered at 1450 °C exhibits a minimum τ_f value of −0.7 ppm/°C.     

Variants of the Bi6TiP2O16 structure: The preparation and crystal structure of the isomorph Bi6(Mn0.6Bi0.4)P2O15

Compounds with the composition Bi₆(Bi_1−yM_y)X₂O_16−z, M = transition metal or Pb, X = P, V, As, display pseudo-tetragonal crystal systems. They are, however, monoclinic with space group I2 and the heavy atom positions mimic the δ-Bi₂O₃ structure. The title compound is monoclinic, a = 11.284(2) Å, b = 5.4259(11) Å, c = 11.112(2) Å, β = 96.25(3)°, I2, Z = 2. Least-squares refinement of single-crystal X-ray diffraction data on F² converged to R1 = 0.050, wR2 = 0.130. The crystal is twinned by two-fold rotation about [0 1 0] and each twin consists of its inverted component forming a racemate. The structure consists of chains of edge sharing (OBi₄) tetrahedra parallel to [1 0 −1]. The chains are bridged parallel to [1 0 1] by linked PO₄ tetrahedra and (Mn/Bi)O₆ octahedra parallel to [1 0 −1], into a three-dimensional structure. The lone-pair electrons of adjacent Bi atoms along the chain point in opposite directions along the b-axis. The Bi atoms are in distorted trigonal prismatic coordination that has one or two faces capped. The BiO bond lengths vary from 2.08(5) to 3.05(2) Å. The Mn/Bi atoms are disordered around the two-fold axis. Three oxygen atom sites contain vacancies.     

Crystal structure of a new organic dihydrogenomonophosphate (C6H8N3O)2(H2PO4)2

Chemical preparation, X-ray single-crystal, thermal behavior, and IR spectroscopy investigations are given for a new organic cation dihydrogenomonophosphate (C₆H₈N₃O)₂(H₂PO₄)₂ (denoted IAHP) in the solid state. This compound crystallizes in the orthorhombic space group P2₁2₁2₁. The unit cell dimensions are: a = 7.422(3) Å, b = 12.568(5) Å, c = 20.059(8) Å with V = 1871.1(13) Å³ and Z = 4. The structure has been solved using direct method and refined to a reliability R factor of 0.029. The atomic arrangement can be described as inorganic layers of H₂PO₄⁻ anions between which are located the organic groups (C₆H₈N₃O)⁺ through multiple hydrogen bonds.     

Microwave dielectric ceramics in (Ca1− xBax)(Zn1 / 3Nb2 / 3)O3 system

(Ca_1−xBa_x)(Zn_1 / 3Nb_2 / 3)O₃ (x = 0–1.0) microwave dielectric ceramics were prepared and investigated. The Ba(Zn_1 / 3Nb_2 / 3)O₃-based solid solution was observed for x = 0.9, and the compositions with x = 0.1–0.7 resulted in the mixture of two phases. Dielectric constant ε_r and temperature coefficient of resonant frequency τ_f of the present ceramics varied anomalously and reached their maximum at x = 0.7–0.9, and these phenomena were originated from the partial substitution of small Ca²⁺ ions for larger Ba²⁺ at A-site. On the other hand, a good combination of microwave dielectric properties (ε_r = 36, Qf = 16,170 GHz, τ_f = − 12 ppm/°C) were obtained at x = 0.1, while the decreased Qf value was observed in other compositions.     

Ba2La2TiTa2O12: A new low loss microwave dielectric of A4B3O12-type cation-deficient perovskite

A new Ta-based hexagonal perovskite Ba₂La₂TiTa₂O₁₂ was synthesized by conventional solid-state reaction method. The structure and microstructure of the ceramic were characterized by X-ray diffraction and scanning electron microscopy. This compound adopts A₄B₃O₁₂ cation-deficient hexagonal perovskite structure with unit cell parameter a = 5.6825(2) Å, c = 27.860(1) Å, V = 779.10 Å³, and Z = 3. This new dielectric ceramic exhibits a moderate dielectric constant of 37.8, a high quality factor with Q × f of 36,188 GHz and a negative τ_f of ?52 ppm/°C.     

Modified giant dielectric properties of samarium doped CaCu3Ti4O12 ceramics

Effects of Sm³⁺ substitution on the microstructure and dielectric properties of CaCu₃Ti₄O₁₂ ceramics were investigated. The grain size of CaCu₃Ti₄O₁₂ ceramics was greatly decreased by doping with Sm³⁺, resulting from the ability of Sm³⁺ to inhibit the grain growth rate. This result can cause a decrease in the dielectric constant (?′) and loss tangent (tan δ) of CaCu₃Ti₄O₁₂ ceramics. Interestingly, high dielectric permittivity (?′ ～ 10,863) and low loss tangent (tan δ ～ 0.043 at 20 °C and 1 kHz) were observed in the Ca_0.925Sm_0.05Cu₃Ti₄O₁₂ ceramic. Nonlinear electrical properties of CaCu₃Ti₄O₁₂ ceramics were modified by doping with Sm³⁺. The dielectric relaxation behavior of Sm-doped CaCu₃Ti₄O₁₂ ceramics can be well ascribed based on the internal barrier layer capacitor model of Schottky barriers at the grain boundaries.     

Microwave dielectric properties of ZnAl2O4–TiO2 spinel-based composites

The microstructures, phase compositions and microwave dielectric properties of ZnAl₂O₄–TiO₂ spinel-based composites have been investigated. It is found that ZnAl₂O₄ cannot form a solid solution with TiO₂. As TiO₂ content increases, the ε_r and τ_f values increase gradually, while the Q · f values degrade by degrees. Under the same amount of TiO₂ content, the ε_r and Q · f values increase initially and then decrease slightly with increasing sintering temperature, while the τ_f values increase slowly. The optimal microwave dielectric properties are achieved in (1 − x)ZnAl₂O₄–xTiO₂ (x = 0.21) sintered at 1500 °C for 3 h with ε_r value of 11.4, Q · f value of 71,810 GHz (at about 6.5 GHz), and τ_f value of − 0.5 ppm/°C.