Synthesis, crystal and electronic structure of BaLi2Cd2Ge2

A new quaternary germanide has been synthesized and structurally characterized. BaLi2Cd2Ge2 adopts the rhombohedral CaCu4P2 structure type (Pearson code hR7; space group R 3 ‾ m $R‾{3}m$ , Z = 3) with unit cell parameters a = 4.5929(6) and c = 26.119(5) Å. Structure refinements from single-crystal X-ray diffraction data demonstrate that the layered crystal structure can be regarded as an ordered quaternary variant of the ternary archetype; structural parallels to layered pnictides and binary germanides can also be drawn. The layered crystal structure is characterized by the absence of direct Ge–Ge and Cd–Cd homoatomic bonds, which suggests that BaLi2Cd2Ge2 should be classified as a Zintl phase, according to the formulation (Ba2+)(Li+)2(Cd2+)2(Ge4−)2. Electronic structure calculations show that the Fermi level crosses a distinct peak in the DOS, although the presence of an electronic band gap or a dip in the electronic density of states at the Fermi level is expected based on the electron partitioning.

Regulating Surface and Local Chemistry in High Na-content P2-type Cathode to Achieve Ultrahigh Power and Low Temperature Sodium Storage

Application of sodium ion batteries in grid-scale energy storage demands electrode materials that facilitate fast and stable charge storage from room-temperature to sub-zero temperature range. The key issues that hinder P2-type layered oxides from achieving such goals are their unsatisfied charge transfer kinetics and unavoidable surface fading. Herein, we report a P2-type Na0.78Ni0.31Mn0.67Nb0.02O2 whereby the trace Nb substitution simultaneously reduces the electronic band gap and ionic diffusion energy barrier, thus enables fast electron and Na+ mobility (~10-9 cm s-1 at -40 °C). While the Nb induced atomic-scale surface pre-construction efficiently prevents the electrolyte penetration and surface metal dissolution. The material demonstrates a record high rate capability (50 C), unprecedented low temperature performance and ultrahigh cycling stability (98% capacity retention at -40 °C with 76% capacity remaining after 1800 cycles). Different from literatures, this work shows that complete solid-solution is not always critical for high rate performance.

Structural and electronic properties of Cu4O3 (paramelaconite): the role of native impurities

Hybrid density functional theory has been used to study the phase stability and formation of native point defects in Cu4O3. This intermediate copper oxide compound, also known as paramelaconite, was observed to be difficult to synthesize due to stabilization issues between mixed-valence Cu1+ and Cu2+ ions. The stability range of Cu4O3 was investigated and shown to be realized in an extremely narrow region of phase space, with Cu2O and CuO forming readily as competing impurity phases. The origin of p-type conductivity is confirmed to arise from specific intrinsic copper vacancies occurring on the 1+ site. Away from the outlined stability region, the dominant charge carriers become oxygen interstitials, impairing the conductivity by creating deep acceptor states in the electronic band gap region and driving the formation of alternative phases. This study further demonstrates the inadequacy of native defects as a source of n-type conductivity and complements existing experimental findings.

DESIGN OF SQUARE MICROSTRIP PATCH MULTI BAND ANTENNA FOR WIRELESS COMMUNICATION USING EBG STRUCTURE

Application of electromagnetic band-gap (EBG) structure and its use in the design of antenna and microwave integrated circuits is becoming more attractive. The recent electromagnetic band-gap structure method is capturing more importance in antenna design due to its uniqueness properties to suppress the propagation of surface waves in microstrip patch antenna. In this paper a square microstrip antenna is designed and its performance parameters are compared with geometry designed on EBG structure. The square antenna of 29 mm x29 mm size is designed at 2.455 GHz and analysis is done using IE3D simulation software. The proposed work mainly focuses on modification of antenna using electronic band gap structure (EBG). The antenna parameters such as Return loss, VSWR, Gain and Bandwidth, with and without EBG are obtained using IE3D simulation tool. The Electromagnetic band-gap structures have been used to improve the performance of the gain of the antennas and radiation patterns. One of the main advantages of electromagnetic band-gap structure is its ability to suppress the surface wave current present on the microstrip antenna. Combining the square patch with EBG structure, the bandwidth of the antenna has been increased by 34.66%, and attained gain of 44.44% at resonant frequency around 2.4 GHz as compared to the antenna without EBG..