SSL Seminar Series 2006 No.1

Date: 16 March (Thursday), 2006
Time: 4:00pm-5:30pm
Venue: Physics Resource Room (Blk S13 # 02-16)

Speaker I: Dr Wu Guotao
Title: Structural Characterization of a New Ternary Imide - Li2Ca(NH)2

Ternary imide Li 2 Ca(NH) 2 was successfully synthesized by mixing LiNH 2 and CaH 2 in a molar ratio of 2:1, and then heating it in a stream of purified argon to 300degC . Powder X-ray diffraction measurement revealed that the Li 2 Ca(NH) 2 was of the trigonal anti-La 2 O 3 structure (space group P-3m1) with lattice constants a = 3.561Å and c = 5.948 Å. Ca occupied 1b site (0, 0, 1/2), Li occupied 2d site (1/3, 2/3, 0.9195), and N occupied 2d site (1/3, 2/3, 0.2303). NMR and XAFS analyses demonstrated that each Li ion was coordinated with 4 imide ions, and each Ca ion was coordinated with 6 imide ions.

Speaker II: Dr Liu Yongfeng
Title: Synthesis and Structural Characterization of a New Alkaline Earth Imide: MgCa(NH)2

The imide MgCa(NH) 2 was first successfully synthesized by the mechanochemical reaction of Mg(NH 2 ) 2 and CaH 2 (molar ratio 1:1). ~4 H atoms gradually detached from the starting chemicals during the mechanical ball milling. FTIR analysis reveals that the solid product exhibits the imide N-H vibration at 3151 cm -1 . A cubic CaNH-like structure was identified by X-ray powder diffraction. In addition, X-ray Absorption Fine Structure examination on Ca confirms that six N atoms occupy the first shell of Ca center in an octahedral geometry, and Ca(Mg) atoms occupy the second shell. The calculated Ca-N and Ca-Ca(Mg) distances in the newly formed MgCa(NH) 2 structure are 2.46 Å and 3.47 Å, respectively.

Speaker III: Dr Liu Tao
Title: How hydrogen affect the spectra features of XANES

The effect of Hydrogen on the structure of some hydroxides and nitrates as probed by X-ray absorption near-edge structure (XANES) spectra were calculated and analyzed by employing the multiple scattering theory. Some general rules were presented for interpreting XANES spectra.