Packing Lattice Research Articles

Mechanical strength and microwave dielectric properties of Al2O3 doped Li2MgTi3O8 ceramics with high temperature stability

A temperature stability microwave dielectric ceramic with composition of Li2MgTi3O8 (LMT) and Al2O3 with high flexural strength is synthesized by a conventional solid-state reaction method. The effects of Al2O3 (particles and whiskers) doping on the mechanical and dielectric properties of LMT ceramics are studied. A single spinel structure, without any secondary phases, is detected in the Al2O3 particles and Al2O3 whiskers doped LMT ceramics. The maximum flexural strengths of 152.5 MPa and 166.73 MPa are delivered in LMT +0.3 wt% Al2O3 (p) ceramics and LMT + 0.3 wt% Al2O3 (w) ceramics, respectively, which are enhanced by 53.21% and 67.52% over those of unmodified LMT ceramics. Pinning and grain refinement contribute to the enhanced flexural strength of the system. The intrinsic factors of Q × f change are analyzed by calculating the packing fraction and lattice energy. In addition, ceramics exhibit excellent comprehensive microwave properties at 1050 °C: (LMT + 0.2 wt% Al2O3 (p):Q × f = 67056 GHz, τf = −8.25 ppm/°C, εr = 24.34, σf = 133.3 MPa; LMT + 0.1 wt% Al2O3(w): Q × f = 68670 GHz, τf = −8.94 ppm/°C, εr = 24.32, σf = 122.7 MPa) The results indicate that Al2O3 particles and Al2O3 whiskers are decent reinforcing agents for LMT ceramics.

NaYW2O8: A novel glass-free microwave dielectric ceramic for LTCC application

Microwave dielectric ceramics are important materials for wireless communication devices because of their excellent dielectric properties. Tungstenate compounds with multiple scheelite structures can be used in low temperature co-fired ceramic (LTCC) devices because of their low densification temperature and high-quality factor. In this study, NaYW2O8 ceramics (NYW) were synthesized by a solid-state reaction method at a low densification temperature below the Ag melting point. The microstructure, morphology and microwave dielectric properties of NYW ceramics were investigated, and the effects of packing fraction and lattice energy on microwave dielectric properties were studied. The results showed that the microwave dielectric properties of NYW ceramics were influenced by the grain size and porosity, and deteriorated with the increase of porosity. In addition, the stacking fraction and lattice energy shared a similar trend with the quality factor. The NYW ceramics sintered at 925 °C exhibited excellent microwave dielectric properties with εr= 10.8, Q × f = 49,800 GHz (at 10.5 GHz), and τf= −26.5 ppm/°C. In particular, the NYW ceramics were found to have an excellent chemical compatibility with Ag. The above results indicate the NYW ceramics are candidate in LTCC applications.

Structural, optical and dielectric properties of chemical vapor transport based synthesis of rice-like nanostructured cadmium zinc oxide films

The cadmium zinc oxide (Cd-ZnO) films are synthesized on glass substrate at 200 sccm argon gas flow rate by chemical vapor transport technique. The synthesized Cd-ZnO films are investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), Raman, Fourier transformed infrared spectroscopy (FTIR) and UV spectrometers. The XRD patterns exhibits the development of various diffraction planes related to Zn, ZnO and CdO phases thereby confirms the formation of polycrystalline Cd-ZnO films. The structural parameters like crystallinity, crystallite size, d-spacing, microstrains, dislocation density, degree of distortion, atomic packing fraction, lattice parameter, bond length and atomic packing factor are associated with increasing weights of Cd powder. The formation of chemical bonding, substitution of Cd+ into ZnO are confirmed by Raman, FTIR and SEM analysis. Red shift in absorption edge and increasing transmittance (> 90%) are associated with increasing weights of Cd powder. Refractive index (2.58–2.63) and energy band gap (3.11–2.87 eV) are increased/decreased with increasing weights of Cd powder. The change in optical, electrical and dielectric parameters of synthesized Cd-ZnO films are strongly associated with increasing weights of Cd powder. Results show that the synthesized Cd-ZnO films can be used for optoelectronics devices.

Bond characteristics and microwave dielectric properties of (Mn1/3Sb2/3)4+ doped molybdate based low-temperature sintering ceramics

Ce2[Zr1−x(Mn1/3Sb2/3)x]3(MoO4)9 (x = 0.1–1.0) ceramics were prepared by a conventional solid-state method. (Mn1/3Sb2/3)4+ ions occupied the Zr-site, and Ce2[Zr1−x(Mn1/3Sb2/3)x]3(MoO4)9 solid solution was obtained. With x value increased, the εr decreased from 10.47 (x = 0.02) to 10.10 (x = 0.10), which was affected by bond ionicity of Zr/(Mn1/3Sb2/3)1O4 bond. The Q·f value first increased and then decreased, which was controlled by varying packing fraction, relative density, and lattice energy (CeO bond). The thermal expansion coefficient and bond energy of MoO bond were associated with τf value. Besides, infrared reflection spectrum suggested that the properties were primarily derived from the absorption of phonon in the infrared range. Outstanding microwave dielectric properties of Ce2[Zr0.92(Mn1/3Sb2/3)0.08]3(MoO4)9 ceramics were obtained when sintered at 700 °C: εr = 10.29, Q·f = 91,981 GHz and τf = −9.81 ppm/°C.

Structure dependence of dielectric characteristics in Li2Mg3Ti1-x(Al0.5Ta0.5)xO6 ceramics

To investigate the effects of (Al0.5Ta0.5)4+ substitution on the crystal structure and dielectric characteristics of Li2Mg3TiO6, a set of Li2Mg3Ti1-x (Al0.5Ta0.5)xO6 (x = 0.0–0.12) samples were fabricated via solid-state process. XRD and Rietveld refinement results confirmed the formation of single rock salt structure in the space group Fm3m (No.225) within 0.0 ≤ x ≤ 0.12. Subsequently, some intrinsic factors were introduced to evaluate the structure dependence of dielectric characteristics in Li2Mg3Ti1-x (Al0.5Ta0.5)xO6 ceramics based on the unit cell parameters. The variation trend of dielectric constant (εr) was explained by the relative density and average ionic polarizability. The quality factor (Q × f) showed the same trend as the packing fraction and lattice energy, indicating the intrinsic lattice anharmonicity might play vital roles in dielectric loss. Additionally, the temperature coefficient of resonant frequency (τf) was strongly associated with the bond energy of Etotal. Typically, the Li2Mg3Ti0.91(Al0.5Ta0.5)0.09O6 sample obtained at 1310 °C possessed remarkable dielectric performances: εr = 15.06, Q × f = 169,600 GHz and τf = −27.45 ppm/°C.

Constituent Isomerism-Induced Quasicrystal and Frank–Kasper σ Superlattices Based on Nanosized Shape Amphiphiles

Naturally, subtle variations in the chemical structures of constituent molecules may significantly affect their multiscale spatial arrangements, properties, and functions. Deceptively simple spheri...

Structural characteristics and dielectric properties of Ti4+-substituted Li2Mg3SnO6 ceramics

To analyze the impacts of intrinsic factors on the dielectric properties, LiF was introduced to eliminate impurity phase Mg2SnO4, and a set of Li2Mg3Sn1-xTixO6-4 wt.% LiF (x = 0.0–1.0) ceramics were prepared by the solid-state reaction method. The XRD and SEM results indicated that all the compositions displayed a pure cubic phase (space group: Fm-3m, 225) and compact microstructure with increasing Ti4+ concentration, accompanied by a decrease in the average crystallite size from 2.54 μm to 1.92 μm. Based on the chemical bond theory and refinement data, several structural factors were determined to evaluate the relationship between the structural characteristics and dielectric properties. The increase in the dielectric constant (εr) was ascribed to the improved average ionic polarizability αth/Vm. The trend of the change in the quality factor (Q × f) was closely related to the packing fraction and lattice energy. Additionally, the temperature coefficient of the resonant frequency (τf) changed within a narrow range, which could be attributed to the minor deviation in the octahedron bond energy. These results demonstrated that structural characteristics are key factors influencing the dielectric properties.

Structure and microwave dielectric properties of Li2Mg3Ti1-x(Al1/2Nb1/2)xO6 ceramics

Aiming to establish relationships between intrinsic structure factors and dielectric characteristics, a series of Li2Mg3Ti1-x(Al1/2Nb1/2)xO6 (x = 0.0, 0.04, 0.08, 0.12, 0.16, 0.20) ceramics were synthesized to investigate the influences of (Al1/2Nb1/2)4+ substitution on the dielectric properties of Li2Mg3TiO6 ceramics. The XRD and SEM results revealed that the pure rock salt phase (space group: Fm-3m) with a dense microstructure could be obtained with increasing the (Al1/2Nb1/2)4+ concentration, which is accompanied by an increase in the grain size from 11.69 to 22.81 μm. Meanwhile, some intrinsic factors, such as the average ionic polarizability, bond energy, packing fraction and lattice energy were calculated according to the complex chemical bond theory and refinement results. The unusual change in the dielectric constant (εr) was explained by the combined effects of the average ionic polarizability and relative density. The variation in the quality factor (Q × f) was ascribed to the packing fraction and lattice energy. The temperature coefficient of the resonant frequency (|τf|) reduced gradually with the increase in the octahedral bond energy, which enhanced the system thermal stability. Particularly, the Li2Mg3Ti0.92(Al1/2Nb1/2)0.08O6 sample exhibited outstanding dielectric characteristics:εr = 15.256, Q × f = 174,300 GHz and τf = −19.97 ppm/°C.

Biogenic capped selenium nano rods as naked eye and selective hydrogen peroxide spectrometric sensor

The Biogenic selenium(0) nano rods were synthesized and stabilized in citric acid and flavonoids from lemon juice by wet chemical route. As synthesized nanorods were characterized using physicochemical analysis techniques as UV–Vis, FITR, PXRD spectrometry, SEM and TEM surface morphology imaging techniques. These nano rods had exhibited trigonal Se packing lattice, 90 nm mean crystallite size and surface capping with flavonoid and citric acid functionality. The Se nanorods show selective sensing of peroxide by visible color change from reddish to faint pink and also through spectrometric sensing plots for concentrations from 60 ppm to 5 ppm with sensing limit up to 75 μM peroxide with interfering cellular cations as K, Na, Ca, Mg and Fe. These biogenic green sensor Se nano rods get converted to nano ovals after surface leaching with peroxide and show SPR based selective sensing mechanism in spectrometric plots. These developed nanorods finds suitable applications in biomedical cellular peroxide sensing with low limits through naked eye cost effective spectrometric sensing method.

Influence of Zn substitution on the crystal structures and microwave dielectric properties of Li2(Mg1-xZnx)3TiO6 (0≤x≤0.2) ceramics

A series of Zn-doped Li2(Mg1-xZnx)3TiO6 (x = 0, 0.05, 0.10, 0.15, 0.2) ceramics were formed via the conventional solid-state process. Influence of Zn2+ on the crystal structures, phase compositions, sintering characteristics and properties of Li2(Mg1-xZnx)3TiO6 (0 ≤ x ≤ 0.2) ceramics were systematically studied. XRD results showed that a single phase with the cubic rock-salt structure was formed for Li2(Mg1-xZnx)3TiO6 (0 ≤ x ≤ 0.15) and the second phase of Zn2TiO4 could be detected with a further increase of the Zn2+ contents. Some intrinsic parameters were calculated in order to investigate the correlations between these parameters of Mg/ZnO bonds and microwave dielectric properties. As the Zn2+ content increases, optimum εr values exhibited an increasing trend, which could be explained by the variations of the polarizability and bond ionicity of Mg/ZnO bonds. The decrease of maximum Q·f values for Li2(Mg1-xZnx)3TiO6 (x = 0, 0.05, 0.10, 0.15, 0.2) ceramics could be predicted by the decrease of the packing fraction and lattice energy of Mg/ZnO bonds. τƒ values showed close relationship with the bond energy and thermal expansion coefficient of Mg/ZnO bonds. Excellent combined microwave dielectric properties with εr = 15.46 (at 10.9 GHz), Q·f = 125,453 GHz (at 8.6 GHz) and τf = −32.35 ppm/°C were obtained for Li2(Mg0.85Zn0.15)3TiO6 ceramic sintered at 1600 °C.

An Efficient Implementation of Lattice Staggered Multicarrier Faster-Than-Nyquist Signaling

In this letter, we investigate the lattice staggered multicarrier faster-than-Nyquist (MFTN) signaling. Specifically, we consider the time–frequency packing and optimal hexagonal lattice over additive white Gaussian noise channels. First, an efficient implementation of the lattice staggered MFTN based on the fast Fourier transform algorithm is proposed, and we show that the modulation and demodulation complexity could be substantially reduced. Furthermore, we consider, at the receiver, a low-complexity symbol-by-symbol detector. Our practical spectral efficiency and bit-error-rate performance investigation demonstrate that the MFTN with optimal hexagonal lattice outperforms the conventional rectangular lattice.

Selective Enclathration of Methyl- and Dimethylpiperidines by Fluorenol Hosts

Two similar fluorenyl diol hosts H1 and H2 have been employed to study their selectivity toward methylated piperidines. Crystal structures show strong similarities in the packing of these inclusion compounds, but the interesting result arises from the competition of these hosts for equimolar dimethylpiperidines (2,6DMP and 3,5DMP). H1 selects 3,5DMP, while H2 selects 2,6DMP. Packing analysis and lattice energy calculations failed to explain this result, but the differential scanning calorimetry profiles of the four host–guest compounds are in agreement with the selectivity experiments.

A Note on Lattice Packings via Lattice Refinements

ABSTRACTRogers proved in a constructive way that every packing lattice Λ of a symmetric convex body K in is contained in a packing lattice whose covering radius is less than 3. By a slight modification of Rogers’ approach better bounds for lp-balls are obtained. Together with Rogers’ constructive proof, this leads, for instance, to a simple o(nn/2) running time algorithm that refines successively the packing lattice Dn (checkboard lattice) of the unit ball Bn and terminates with a packing lattice with density . We have also implemented this algorithm and in small dimensions (⩽ 25) and for certain simple structured start lattices like or Dn the algorithm often terminates with packing lattices achieving the best-known lattice densities.

Correlation of crystal structure and microwave dielectric characteristics of temperature stable Zn1−xMnxZrNb2O8 (0.02≤x≤0.1) ceramics

Wolframite-structured Zn1−xMnxZrNb2O8 (x=0.02, 0.04, 0.06, 0.08, 0.10) ceramics were synthesized by the conventional solid-state method. The effects of Mn2+ substitution on the crystal structure, crystal chemistry and microwave dielectric properties of ZnZrNb2O8 were investigated. Bond ionicity, lattice energy and thermal expansion of the ceramics were calculated by the complex chemical bond theory, which were used to investigate the correlation between intrinsic factors and microwave dielectric properties. The εr values were dependent on the electronic oxide polarizabilities of Zn1−xMnxZrNb2O8 ceramics. The Q·f values decreased from 51,300 to 44,900GHz, which could be explained in terms of packing fraction and lattice energy. The τf values were shifted to positive direction with the increase of Mn2+ contents, which indicated that the distortion of the [BO6] octahedral was closely related to τf values. In addition, thermal expansion coefficient also affected the temperature stability of ceramics. Typically, an excellent microwave dielectric property was obtained in the Zn0.9Mn0.1ZrNb2O8 with a εr of 29.43, an appropriate Q·f of 44,900GHz and a near zero τf of −5.61ppm/°C.

Hexagonal packing lattice formed by functionalized gold nanoparticles

Nanostructures formed by functionalized gold nanoparticles (GNPs) were studied using X-ray diffraction (XRD). Two systems of such functionalized GNPs, one with gold core grafted by both ligand (rod-like liquid crystalline molecule) and co-ligand (alkylthiols) and the other one with only ligand grafted, were studied. The presence of ligands and co-ligands increases the mobility of GNPs and induces long-range ordered packing style with the change of temperature. In both systems, functionalized GNPs form columns first and then pack on hexagonal lattice. It is found that the correlation along column direction is dependent on surface conditions of GNPs, which is observed for system with only ligand grafted. Based on experimental results, size of gold core and number of ligand and co-ligand belonging to each gold core were calculated. Diffraction intensities and electron density map of each structure were simulated, which are evidently similar to experimental ones. Finally, structure model was proposed and discussed. The results help us to understand and control the way that organic molecules affect the organization of nanoparticles, and facilitate the design of new hybrid materials. Gold nanoparticles (yellow) functionalized by liquid crystalline ligand (green) and co-ligand (red) can form ordered 3D hexagonal columnar phase. In this structure, ligands congregate around the equator of the gold nanoparticles, while co-ligands aggregate near the north and south poles. This enables the nanoparticles to align in strings wrapped in the sheaths of uniaxially oriented mesogens forming columns, and then these columns are packed on a hexagonal lattice.

Constellation choosing based on multi-dimensional sphere packing technique

In this paper we address the sphere packing lattice points selection problem being used as constellation points in high-dimensional modulation. We propose a new type of points selection method based on threshold theory. Theoretically, this method improves the transmission performance of high-dimensional signal modulation systems. We find that the BER of a 4D modulation signal using the threshold value points selection method reduces. We also compared random and distant points selection methods in a BER of 10−3 and obtained a reduced SNR of about 2db. At a 10−3 BER, a 8D modulation signal with points selected using the threshold selection methods obtained a reduced SNR of about 3db. At a 10−3 BER, a 16D modulation signal with points selected using the threshold selection methods obtained a reduced SNR of about 3.5db.

Structural, thermal and optical properties of KTi0.92La0.08OPO4 and KTi0.94Nd0.06OPO4

KTi0.92La0.08OPO4 (KTP:La) and KTi0.94Nd0.06OPO4 (KTP:Nd) single crystals are grown using high temperature top seeded flux growth technique. The strain derived from doping is calculated from Williamson–Hall relation. The packing structure and lattice parameter of the grown crystals are analyzed using single crystal X-ray diffraction. The bonding, distortion and change in inter-atomic distances by strain effects of doping are assessed by Raman spectroscopy. Thermal stabilities of grown crystals are evaluated by specific heat capacity measurement. Pronounced high specific heat capacity is recorded as 1.16J/gK at 498K for KTP:Nd. Second harmonic generation intensities are measured for KTP:Nd and KTP:La single crystal.

DPPC Monolayers Exhibit an Additional Phase Transition at High Surface Pressure

Pulmonary surfactant forms a monolayer at the air/aqueous interface within the lung. During the breath process, the surface pressure (Π) periodically varies from ∼40mN/m up to ∼70mN/m. The film is mechanically stable during this rapid and reversible expansion.Pulmonary surfactant consists of ∼90% of lipid with 10% integrated proteins. Among its lipid compounds, di-palmitoyl-phosphatidylcholine (DPPC) dominates (∼45wt%). DPPC is the only known lipid that can be compressed to very high surface pressure (∼70mN/m) before its monolayer collapses. Most probably, this feature contributes to the mechanical stability of the alveoli monolayer. Still, to the best of our knowledge, some details of the compression isotherm presented here and the related structures of the DPPC monolayer were not studied so far.The liquid-expanded/liquid-condensed phase transition of the DPPC monolayer at ∼10mN/m is well known. Here, we report a second phase transition at elevated surface pressure (∼50mN/m). The lateral structure of the monolayer at selected states (8mN/m, 20mN/m, 30mN/m, 40mN/m, 50mN/m, 60mN/m, 70mN/m; covering the whole pressure range of the isotherm) was investigated by grazing incidence X-ray diffraction (GIXD). The results report on the 2D packing lattice and on the inter-chain distance dxy. Moreover, the tilt angle of the palmitoyl chains was calculated combining the lattice parameters and the geometrical boundary conditions. The course of the inter-chain distance versus surface pressure exhibits two regimes, separated by the phase transition.

An Amino Acid Packing Code for α-Helical Structure and Protein Design

This work demonstrates that all packing in α-helices can be simplified to repetitive patterns of a single motif: the knob–socket. Using the precision of Voronoi Polyhedra/Delauney Tessellations to identify contacts, the knob–socket is a four-residue tetrahedral motif: a knob residue on one α-helix packs into the three-residue socket on another α-helix. The principle of the knob–socket model relates the packing between levels of protein structure: the intra-helical packing arrangements within secondary structure that permit inter-helix tertiary packing interactions. Within an α-helix, the three-residue sockets arrange residues into a uniform packing lattice. Inter-helix packing results from a definable pattern of interdigitated knob–socket motifs between two α-helices. Furthermore, the knob–socket model classifies three types of sockets: (1) free, favoring only intra-helical packing; (2) filled, favoring inter-helical interactions; and (3) non, disfavoring α-helical structure. The amino acid propensities in these three socket classes essentially represent an amino acid code for structure in α-helical packing. Using this code, we used a novel yet straightforward approach for the design of α-helical structure to validate the knob–socket model. Unique sequences for three peptides were created to produce a predicted amount of α-helical structure: mostly helical, some helical, and no helix. These three peptides were synthesized, and helical content was assessed using CD spectroscopy. The measured α-helicity of each peptide was consistent with the expected predictions. These results and analysis demonstrate that the knob–socket motif functions as the basic unit of packing and presents an intuitive tool to decipher the rules governing packing in protein structure.

Crystallographic Realization of the Mathematically Predicted Densest All‐Pentagon Packing Lattice by C5‐Symmetric “Sticky” Fluoropentamers

Crystallographic Realization of the Mathematically Predicted Densest All‐Pentagon Packing Lattice by <i>C</i>₅‐Symmetric “Sticky” Fluoropentamers