The electronic and magnetic properties of (Mn,N)-codoped ZnO are studied within the framework of the density functional theory, by using the Perdew–Burke–Ernzerhof form of generalized gradient approximation. Five geometrical configurations of Mn doped ZnO are investigated and antiferromagnetic (AFM) properties of Mn doped ZnO are demonstrated. Furthermore, by investigating 13 geometrical configurations, for (Mn,N)-codoped ZnO, the ground state is changed from no-metallic AFM to half-metallic ferromagnetic, which is due to the strong hybridization between N 2p and Mn 3d states. In addition, the most stable configurations are found to be –O–Mn–N–Mn–O–.
The effects of water vapor dilution on autoignition and detonation development induced by an ignition spot with thermal non-uniformity in an n-C7H16/air mixture are numerically investigated. Zero-dimensional homogeneous ignition under constant-volume conditions is studied first. It is found that excitation time increases, whereas total heat release decreases with a H2O vapor mole fraction. Moreover, the role of H2O vapor diluents as a third body considerably influences the critical temperature gradient. One-dimensional autoignition and detonation development caused by temperature gradients in ignition spots is then studied. Three different autoignition modes are identified: (I) supersonic deflagrative wave, (II) detonative wave, and (III) subsonic deflagrative wave. It is found that H2O dilution has a slightly better performance on detonation suppression than CO2 dilution. The chemistry–acoustics interactions during autoignition development are weakened when the H2O mole fraction is increased. Besides, H2O vapor dilution can delay the detonation initiation and reduce detonation intensity. Furthermore, typical autoignition processes induced by a hotspot and the chemical effects of water vapor diluent are discussed. It is seen that the chemical effects of H2O dilution do not affect the lower limits of detonation development curves. Besides, the third body effect from the H2O vapor diluent is important in suppressing the detonation development for the investigated ignition spot size. Finally, the effects of equivalence ratios and ignition spot sizes on the autoignition modes of n-C7H16/air/H2O mixtures are studied. It is observed that the water vapor diluted mixtures with the fuel-lean condition are advantageous in inhibiting detonation from localized thermal non-uniformity.
Chemical method was employed to synthesize Mn and Al codoped ZnO, namely, Zn0.995−xMn0.005AlxO with the nominal composition of x=0, 0.005, and 0.02. Structural, optical, and magnetic properties of the produced samples were studied. The results indicated that introduce Al as additional dopants induces in an enhancement of the ferromagnetism in Zn0.995Mn0.005O. The enhanced ferromagnetism (FM) in (Mn,Al) codoped sample can be understood in view of that introducing of Al could promote spinodal decomposition and lead to Mn rich regions. The Mn rich regions could be responsibility for the observed enhancement of FM at room temperature.
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