Chuanmin Meng

High pressure treated ZnO ceramics towards giant dielectric constants

ZnO ceramics with giant dielectric constants have been synthesized via a high pressure treating method. SEM results reveal that the ceramics using high pressure treated powders are porous, and the dielectric constant of the specimens first increases and then decreases with increasing density. Ceramics sintered at 1050 °C possess the optimal giant room temperature dielectric constants (∼1.8 × 104 at 100 Hz) with low relative density and dielectric loss. The improved dielectric constant can be attributed to enhanced Maxwell–Wagner poly-dispersive relaxation due to the high pressure treating process, which makes ZnO porous ceramics a potential material for high dielectric constant applications. This approach is generic and provides a new avenue to obtain porous ceramics with excellent dielectric properties.

Fabrication of uniform Ge-nanocrystals embedded in amorphous SiO2 films using Ge-ion implantation and neutron irradiation methods

[Chen, Q.; Lu, T.; Hu, Y.] Sichuan Univ, Dept Phys, Chengdu 610064, Peoples R China. [Chen, Q.; Lu, T.; Hu, Y.] Sichuan Univ, Key Lab Radiat Phys & Technol Minist Educ, Chengdu 610064, Peoples R China. [Xu, M.] Sichuan Normal Univ, Inst Solid State Phys, Chengdu 610068, Peoples R China. [Xu, M.] Chinese Acad Sci, Int Ctr Mat Phys, Shenyang 110016, Peoples R China. [Meng, C.] China Acad Engn Phys, Inst Fluid Phys, Key Lab Shock Wave & Detonat Phys Res, Mianyang 621900, Peoples R China. [Sun, K.] Univ Michigan, Dept Mat Sci & Engn, Ann Arbor, MI 48109 USA. [Sun, K.] Univ Michigan, Elect Microbeam Anal Lab, Ann Arbor, MI 48109 USA. [Shlimak, I.] Bar Ilan Univ, Dept Phys, Minerva Ctr, IL-52900 Ramat Gan, Israel. [Shlimak, I.] Bar Ilan Univ, Jack & Pearl Resnick Inst Adv Technol, IL-52900 Ramat Gan, Israel.;Chen, Q (reprint author), Sichuan Univ, Dept Phys, Chengdu 610064, Peoples R China;lutiecheng@scu.edu.cn hsuming_2001@yahoo.com.cn

Shock-induced cation disorder in magnesium aluminate spinel

An increase in lattice constants and an order-disorder phase transition were observed in the magnesium aluminate spinel (MgAl(2)O(4)) powders after shock compression. Theoretical calculations on the basis of density functional theory confirm that the remarkable volume expansion in shocked MgAl(2)O(4) powders is closely related to the substantial site disorder in the MgAl(2)O(4) lattice. The calculations also show that the partially inverse MgAl(2)O(4) spinel with an inversion index of 0.7 represents the greatest disordered metastable phase and the most unstable structure

Fabricating Ohmic contact on Nb-doped SrTiO3 surface in nanoscale

Fabricating reliable nano-Ohmic contact on wide gap semiconductors is an important yet difficult step in oxide nanoelectronics. We fabricated Ohmic contact on the n-type wide gap oxide Nb-doped SrTiO3 in nanoscale by mechanically scratching the surface using an atomic force microscopy tip. Although contacted to high work function metal, the scratched area exhibits nearly linear IV behavior with low contact resistance, which maintains for hours in vacuum. In contrast, the unscratched area shows Fowler–Nordheim tunneling dominated Schottky rectifying behavior with high contact resistance. It was found that the Ohmic conductivity in the scratched area was drastically suppressed by oxygen gas indicating the oxygen vacancy origin of the Ohmic behavior. The surface oxygen vacancy induced barrier width reduction was proposed to explain the phenomena. The nanoscale approach is also applicable to macroscopic devices and has potential application in all-oxide devices.

Synthesis of CsCl-type single-phase RuSi under shock compression

Shock recovery experiments were performed on ruthenium–silicon powder mixtures by a flyer plate impact technique. The flyer velocities were in the range of 0.46–2.73 km/s, and the incident shock pressures were calculated to be ∼2.9–∼40.4 GPa by the impedance matching method. The recovered samples were characterized by X-ray diffraction and scanning electron microscopy. Results indicate that shock could induce a reaction between ruthenium and silicon. The shock pressure was found to affect reaction kinetics and microstructure of the recovered sample significantly. The dynamic reaction has a threshold pressure, and the samples loaded above threshold pressure almost completely reacted to a single-phase intermetallic compound of CsCl-type RuSi. These results indicate that shock compression could be an effective way to synthesize RuSi.