Aberration-corrected scanning transmission electron microscopy for complex transition metal oxides

Lattice,charge,orbital,and spin are the four fundamental degrees of freedom in condensed matter,of which the interactive coupling derives tremendous novel physical phenomena,such as high-temperature superconductivity（high-T_c SC） and colossal magnetoresistance（CMR） in strongly correlated electronic system.Direct experimental observation of these freedoms is essential to understanding the structure-property relationship and the physics behind it,and also indispensable for designing new materials and devices.Scanning transmission electron microscopy（STEM） integrating multiple techniques of structure imaging and spectrum analysis,is a comprehensive platform for providing structural,chemical and electronic information of materials with a high spatial resolution.Benefiting from the development of aberration correctors,STEM has taken a big breakthrough towards sub-angstrom resolution in last decade and always steps forward to improve the capability of material characterization;many improvements have been achieved in recent years,thereby giving an indepth insight into material research.Here,we present a brief review of the recent advances of STEM by some representative examples of perovskite transition metal oxides;atomic-scale mapping of ferroelectric polarization,octahedral distortions and rotations,valence state,coordination and spin ordering are presented.We expect that this brief introduction about the current capability of STEM could facilitate the understanding of the relationship between functional properties and these fundamental degrees of freedom in complex oxides.

Synthesis,Electrochemical and Fluorescent Properties of a New Zinc(Ⅱ) Complex through Self-assembly Reaction of 2,2'-Bipyridine-3,3'-dicarboxylic Acid

A new Zn（Ⅱ） complex [Zn（Phen）2（C（12）H6O4N2）（H2O）]·3H2O with 2,2-bipyridine-3,3-dicarboxylic acid and 1,10-phenanthroline（Phen） as ligands was synthesized, and the crystal data are as follows： monoclinic, space group P2（1/n）, a=12.5581（11）, b=17.3382（17）, c=15.6687（14） , β=110.579（2）o, Mr=731.02, V=3193.9（5） 3, Dc=1.520 g/cm3, Z=4, μ（Mo Kα）=0.833 mm（-1）, F（000）=1508, the final R=0.0431 and w R=0.0936. In the title complex, the central Zn（Ⅱ） ion is located in a distorted octahedral coordination environment. The electrochemical and fluorescent properties were studied. The title complex possesses irreversible electron transfer in the electrode reaction, and it has a strong emission peak in the range of 470505 nm, with the excitation wavelength being 488 nm.

Hydrothermal Synthesis,Crystal Structure and Properties of a New Copper(Ⅱ) Coordination Polymer with 3-(2-Pyridiyl)-1H-1,2,4-triazole(Hpt)

A new copper（Ⅱ） coordination polymer [Cu2（C7H5N4）2（3-C6H5NO2）2]n（1） has been hydrothermally synthesized with copper hydroxide, 3-（pyridin-2-yl）-1,2,4-triazole（Hpt） and 3-pyridinecarboxylic acid（3-PCA）. It crystallizes in the monoclinic space group C2/c, with a=16.854（2）, b=7.8616（8）, c=20.630（2） , β=111.126（2）o, V=2549.7（5） 3, Dc=1.723 g/cm3, Z=8, F（000）=1336, the final GOOF=1.065, R=0.0380 and w R=0.0972. The whole molecule consisting of two copper ions are bridged by two μ2-η1：η0-3-（pyridin-2-yl）-1,2,4-triazole anions. The coordination environment of Cu（1） ion is CuO2N4, giving a distorted octahedron geometry. 1 exhibits antiferromagnetic interaction, and the electron transfer of 1 is irreversible in electrode reactions and the TG analysis shows that 1 is stable below 235 ℃.

Influence of Organic Cations on the Crystal and Electronic Structures of Two-dimensional Lead Iodide Perovskites

The crystal structures and electronic structures(including band gap,project density of states,partial charge density,effective mass and electron localization function)of the 2D lead iodide perovskites hybrids with different organic spacer cations of 4-fluorophenylethanaminium(4F-PEA^(+)),ethanolamine(EA^(+)),thienylethylamine(TEA^(+))were investigated using first-principles calculations.It was found the higher dipole moment,the stronger the hydrogen bonding between the organic amino and iodide in the inorganic layer,and the larger the[PbI_(6)]^(4-)octahedral distortions in these crystal structure.Further quantifying the degree of the distortions using OctaDist software showed that the distortion of adjacent[PbI_(6)]^(4-)octahedra had a decisive effect on the band gap.Specifically,the greater deviation of Pb-I-Pb bond angles from 180°,together with the larger distortion of multiple[PbI_(6)]^(4-)octahedron resulted in a wider band gap,which was verified by calculated band gap using different DFT methods.The results outlined the relationships of hydrogen bonding,ocathedra distortion and band structure in 2D perovskites,highlighting the importance of the cations on the structural tuning and optoelectronic properties.

Synthesis and crystal structure of a Ni(II) complex with 1,7-diaminoethyl-4,10-dimethyl-1,4,7,10-tetraazacyclododecane

The crystal structure of a Ni(II) complex with 1,7-diaminoethyl-4,10-dimethyl,4,7,10-tetraazacyclododecane has been determined by X-ray diffraction method. Crystal data for NiC14H36Br2N6O: monoclinic, space group P21/n, a=0.8848(3), b=1.4656(3), c=1.5828(3) nm, β=90.47(3)°, V=2.0525 nm3, Z=4. The two pendant primary amino groups are located in cis positions in the complex, their nitrogen atoms and the four nitrogen donors of the fold tetraaza-macrocycle coordinate Ni(II) ion, forming a distorted octahedral geometry.

Microwave dielectric high-entropy ceramic Li(Gd_(0.2)Ho_(0.2)Er_(0.2)Yb_(0.2)Lu_(0.2))GeO_(4) with stable temperature coefficient for low-temperature cofired ceramic technologies

High-entropy ceramics are new single-phase materials with at least four cation or anion types.Their large configurational entropy is believed to enhance the simultaneous solubility of many components,which can be used to optimize certain properties.In this work,a high-entropy oxide,Li(Gd_(0.2)Ho_(0.2)Er_(0.2)Yb_(0.2)Lu_(0.2))GeO_(4)(LRG)was explored as a microwave dielectric ceramic for lowtemperature cofired ceramic technologies.The LRG high-entropy ceramic with an olivine structure formed in the sintering temperature range of 1020-1100℃.The minimal distortion(5×10^(-4))of the[RO_(6)]octahedron led to a stable temperature coefficient of resonant frequency(τf)of-5.3 to-2.9 ppm/℃.Optimal microwave dielectric properties were achieved in the high-entropy ceramics at 1080℃ for 4 h with a relative density of 94.9%,a relative permittivity(ε_(r))of 7.2,and a quality factor(Q×f)of 29000 GHz(at15.3 GHz).For low-temperature cofired ceramic technology applications,the sintering temperature of the LRG high-entropy ceramic was reduced to 900℃ by the addition of 3 wt%H_(3)BO_(3),which exhibited outstanding microwave dielectric properties(ε_(r)=7.6,Q×f=11700 GHz,and τ_(f)=-7.4 ppm/℃)and a good chemical compatibility with silver.

DEPENDENCE OF MICROWAVE DIELECTRIC PROPERTIES ON STRUCTURAL CHARACTERISTICS OF ILMENITE,TRI-RUTILE AND WOLFRAMITE CERAMICS

Effects of crystal structures on dielectric properties of ATiO_(3)(trigonal ilmenite),ATa_(2)O_(6)(tetragonal tri-rutile)and AWO_(4)(monoclinic wolframite)(A=Ni,Mg,Co)ceramics with A-and B-site oxygen octahedra were investigated at microwave frequencies.The dielectric constant(K) of the specimens was affected by the dielectric polarizabilities of composition and cation bond valence between octahedral cation and oxygen ion per molar volum(V_(m)).The quality factor(Qf)of ATiO_(3)was appreciably larger than those of ATa_(2)O_(6)and AWO_(4)due to the different sharing types of oxygen octahedra.The temperature coe±cient of resonant frequency(TCF)of the specimens was dependent on the octahedral distortion per V_(m).