Abstract.A 298i and 27A1 magic angle spinning nuclear magnetic resonance study is reported for differently synthesized mullites. The 298i MAS NMR spectra of all samples are essentially identical. They consist of a main resonance at -86.8 ppm, a shoulder around -90 ppm and a second resonance at -94.2 ppm. The main resonance is interpreted as being due to a sillimanite-type geometry around Si and the second one is tentatively assigned to a Si environment typical for mullite. The 27A1 MAS NMR spectra of sinter-and fused-mullite measured at different Larmor frequencies revealed clearly the presence of three distinct A1 sites in mullite, i.e. of octahedral (M1), tetrahedral (M2) and distorted tetrahedral (AI*) sites.
An EPR study of F$+ centres in single crystals of KTiOP04 (KTP) has been performed. Twocrystalsgrownunderidenticalconditionshave been usedintheexperiment carried out at the Q-band frequency: the first was imn doped and the other was undoped. Four Fe3+ centres have been observed. All spin-Hamiltonian parameters Were calculated for the four centres. Comparison of the pseudosymmetries obtained from fourthirrder constants of the spin Hamiltonian and from a fourth-order crystal-field calculation for the W O Ti octahedra allowed us to locale two Fe3* centres at each Ti site in KIP. The absence of astrongaxialdeviationfromcubicsymmetryshowsthdt thechargecompensationmechanism is not at short distance for the four centres. All four cenres denoted as ST1, ST2, ST3 and ST4 are present in the iron-doped crystal but only one (ST4) is observable in the undoped crystal. In the undopedcrystal,alsoCr" wasobserved. Resultsfor r h e C P c e n t r e s a r e g n and compared with those already reported by Hasanova and co-workers.
The 35CI-NQR spectra of 45 chlorosubstituted acetanilides, ClxCBH,_,NHCOCH,_,CI,, were investigated and the temperature dependence of some spectra, especially of monochloroacetic acid derivatives, was measured. A preliminary assignment of the NQR frequencies is given. A correlation between NQR frequencies and substituent parameters permits the study of the substituent effect of the acetamido group, -NHCOCH,-yCIY. The chloro-substitution in the side chain of the acetanilides seems to have no noticeable influence on the Wl-NQR frequencies of the chlorine atoms at the benzene ring. The NQR frequencies of the chlorine atoms in the chloroacetamido group arc, on the other hand, insensitive to substitutions at the benzene nucleus. The possibility of steric influences on the NQR spectrum of ortho-chloro-substituted acetanilides is discussed. The investigation further confirms that a crystal field effect of about 5500 kHz must be considered in the interpretation of NQR spectra of chlorobenzene derivatives.
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