Complex Bond Theory Research Articles

The relationship between the bond ionicity, lattice energy, bond energy and microwave dielectric properties of LaNbO4 ceramics

LaNbO4 ceramics with single monoclinic fergusonite structure were prepared by the conventional solid-state reaction method at the sintering temperature range of 1275–1375 °C. The correlations of bond ionicity, lattice energy, bond energy and the microwave dielectric properties were investigated. The bond ionicity, lattice energy, and bond energy were calculated based on the complex bond theory to analyze the variation trend of dielectric constant (er), the Q × f0 value and the temperature coefficient of resonant frequency (τf), respectively. LaNbO4 ceramics sintered at 1350 °C for 4 h possessed excellent microwave dielectric properties: er = 21, Q × f0 = 55600 GHz and τf = 8 ppm/°C.

Crystal structure and microwave dielectric properties of Ta5+ substituted MgZrNb2O8 ceramics

Abstract The MgZr(Nb 1−x Ta x ) 2 O 8 (0 ≤ x ≤ 0.1) ceramics were synthesized through the conventional solid-state process. Pure phase with the monoclinic wolframite structure was observed in all range. The bond ionicity, lattice energy and bond energy of MgZr(Nb 1−x Ta x ) 2 O 8 ceramics were calculated based on the complex bond theory in order to investigate the correlations between microwave dielectric properties and structural characteristics. The substitution of Ta 5+ for Nb 5+ in MgZr(Nb 1−x Ta x ) 2 O 8 ceramics visibly improved the quality factor and the samples with x = 0.1 sintered at 1300 °C for 4 h exhibited excellent microwave dielectric properties: e r = 23.16, Q × f = 88,440 GHz, τ f = −47.65 ppm/°C.

Characterization of low loss CoTiNb2O8 microwave dielectric ceramics based on the complex bond theory

The tetragonal-structured CoTiNb2O8 was prepared by the conventional solid-state method. Morphology, crystal structure and microwave dielectric properties of the ceramics were investigated by means of scanning electron microscope and X-ray diffraction. Single-phase CoTiNb2O8 could be obtained in the temperature range of 1100–1200 °C with the space group of P42/mnm. The dielectric constant and quality factors gradually increased with the increase of apparent density. The τ f values were shifted toward zero with the increase of sintering temperature. Complex bond theory was reported for the first time to characterize the correlations between crystal structure and microwave dielectric properties. Typically, the saturated samples sintered at 1150 °C exhibited excellent microwave properties with e r value of 66.41, Q·f value of 10,153 GHz and τ f value of 25.56 ppm/°C.

Characterization of crystal structure and microwave dielectric properties of AZrNb2O8 (A=Zn, Co, Mg, Mn) ceramics based on complex bond theory

Single phase AZrNb2O8 (A=Zn,Co,Mg,Mn) ceramics with monoclinic wolframite structure were prepared and characterized by crystalline structure refinement for the investigation on the correlations between crystal structure and microwave dielectric properties. A semiempirical method based on the complex bond theory was used to calculate the bond ionicity, lattice energy, and coefficient of thermal expansion of AZrNb2O8 ceramics. The crystal structure changed with the variation of A site ions and affected the Nb–O octahedral correspondingly. Due to the variation of crystal structure, the observed bond ionicity was helpful to understand the electric polarization. The variation of the Q·ƒ and τƒ values could be attributed to the lattice energy and coefficient of thermal expansion respectively. The microwave properties of AZrNb2O8 ceramics were strongly dependent on the chemical bond ionicity, lattice energy and coefficient of thermal expansion.

Correlations of crystal structure, bond energy and microwave dielectric properties of AZrNb2O8 (A = Zn, Co, Mg, Mn) ceramics

The monoclinical structure AZrNb2O8 (A = Zn, Co, Mg, Mn) ceramics were prepared by the conventional solid-state method. The microwave dielectric properties of AZrNb2O8 (A = Zn, Co, Mg, Mn) ceramics exhibited significant dependence on the sintering conditions, microstructure and compositions. The crystalline structure refinement, chemical bond ionicity, lattice energy were carried out to investigate the correlations between the crystalline structure and microwave dielectric properties for AZrNb2O8 (A = Zn, Co, Mg, Mn) ceramics based on the complex bond theory. The effects of A-site cations (Mn, Zn, Mg and Co) at AZrNb2O8 compounds on structural parameters such as packing fraction and B-site octahedral distortion were studied based on Rietveld refinement. Variations in the dielectric constant (εr) were explained by the ionic polarizability of the compositions. The quality factor (Q·ƒ) and temperature coefficient of resonant frequency (τf) were correlated with the packing fraction and B-site octahedral distortions (δ) in these compositions, respectively. Correlations between the microwave dielectric properties and crystal structure, the chemical bond energy were also discussed based on the variation of A-site ions.

The relationship between bond ionicity, lattice energy, coefficient of thermal expansion and microwave dielectric properties of Nd(Nb(1-x)Sb(x))O4 ceramics.

The crystalline structure refinement, chemical bond ionicity, lattice energy and coefficient of thermal expansion were carried out for Nd(Nb(1-x)Sb(x))O4 ceramics with a monoclinic fergusonite structure to investigate the correlations between the crystalline structure, phase stability, bond ionicity, lattice energy, coefficient of thermal expansion, and microwave dielectric properties. The bond ionicity, lattice energy, and coefficient of thermal expansion of Nd(Nb(1-x)Sb(x))O4 ceramics were calculated using a semiempirical method based on the complex bond theory. The phase structure stability varied with the lattice energy which was resulted by the substitution constant of Sb(5+). With the increasing of the Sb(5+) contents, the decrease of Nb/Sb-O bond ionicity was observed, which could be contributed to the electric polarization. The ε(r) had a close relationship with the Nb/Sb-O bond ionicity. The increase of the Q×f and |τ(f)| values could be attributed to the lattice energy and the coefficient of thermal expansion. The microwave dielectric properties of Nd(Nb(1-x)Sb(x))O4 ceramics with the monoclinic fergusonite structure were strongly dependent on the chemical bond ionicity, lattice energy and coefficient of thermal expansion.