SrBi2-χNdχNb2O9(χ=0,0.1,0.2 and 0.4)bismuth layer-structured ferroelectric ceramics were prepared by the solid-state reaction sintering method.The accurate position of Nd element in SrBi2-χNdχNb2O9 ceramics was determined by the X-ray Rietveld method and Synchrotron radiation X-ray absorption fine structure(XAFS)technology.The partial substitution of Nd 3+ for Bi 3+ leads to the decrease in the distortion of NbO6 octahedron for SrBi2-χNdχNb2O9 ceramics and also lowers the piezoelectric properties of SrBi2-χNdχNb2O9 ceramics.Meanwhile,the temperature coefficient of resonant frequency(TCF)decreases when Nd element partially replaces Bi element in SrBi2-χNdχNb2O9 ceramics.
Based on our previous work,the influence of annealing conditions on impurity species in in-situ arsenic (As)-doped Hg 1 x Cd x Te (x ≈ 0.3) grown by molecular beam epitaxy has been systematically investigated by modulated photoluminescence spectra.The results show that (i) the doped-As acting as undesirable shallow/deep levels in as-grown can be optimized under proper annealing conditions and the physical mechanism of the disadvantage of high activation temperature,commonly assumed to be more favourable for As activation,has been discussed as compared with the reports in the As-implanted HgCdTe epilayers (x ≈ 0.39),(ii) the density of V Hg has an evident effect on the determination of bandgap (or composition) of epilayers and the excessive introduction of V Hg will lead to a short-wavelength shift of epilayers,and (iii) the V Hg prefers forming the V Hg-As Hg complex when the inactivated-As (As Hg or related) coexists in a certain density,which makes it difficult to annihilate V Hg in As-doped epilayers.As a result,the bandedge electronic structures of epilayers under different conditions have been drawn as a brief guideline for preparing extrinsic p-type epilayers or related devices.
Variable-temperature transmission/absorption spectra are measured on As-doped Hg 1 x Cd x Te grown by molecular beam epitaxy.The nonlinear temperature-dependent shift of the absorption edge is also observed,which is similar to our previous report on V Hg (unintentionally)-doped HgCdTe.By referring to the empirical formulas of E g (x,T),the x value of the epilayer is calculated and its inconsistency between the extreme temperatures (e.g.10 and 300 K) is discussed.The results confirm the assumption of the effect of shallow levels on the shift of the absorption edge,and suggest that the x value (or E g) in intrinsic/extrinsic-doped HgCdTe should be determined by referring to as low a temperature as possible (e.g.10 K),and not the commonly used temperatures of 77 or 300 K,when the transmission spectrum should be employed.This can give brief guidelines for fabricating HgCdTe-related devices.
