The synthesis and structure of a new zeolite, CIT-5 (California Institute of Technology Number Five), is described, which possesses one-dimensional pores comprised of 14 T-atoms (tetrahedrally coordinated silicon or aluminium atoms).Zeolites with pores comprised of larger than 12 T-atoms (extralarge pores) are much in demand 1-4 and have been so for many years. [4][5][6][7] The reason for this is the desire to perform catalysis/ adsorption on molecules > 8 Å in size.The first molecular sieve with extra-large pores was VPI-5 that is an aluminophosphate material with 18-ring pores. 8 Subsequently, other phosphate-based extra-large pore materials have been reported, e.g. cloverite. 2 All of the phosphate-based molecular sieves lack the desired properties of combined high acidity and thermal/hydrothermal stability and thus limit the practical potential. Recently, the first extra-large pore zeolite, UTD-1, was reported and shown to possess good acidity and thermal/hydrothermal stability. 9,10 Additionally, there have been numerous disclosures of ordered, aluminosilicate mesoporous materials with pore sizes of 20-100 Å. 11,12 Because the inorganic portions of the mesoporous materials are not crystalline, they lack the acidity and thermal/hydrothermal stability of high-silica zeolites. 13 Here, we report a new extra-large pore zeolite denoted CIT-5. CIT-5 is synthesized under hydrothermal conditions. A reaction mixture of composition 0.2 ROH : 0.1 LiOH : 0.02 Al 2 O 3 : 1 SiO 2 : 40 H 2 O is heated to 175 °C at autogenous pressure for ca. 12 d in order to produce CIT-5. In the absence of aluminium, pure-silica CIT-5 can be prepared in 5 d. The organic structuredirecting agent (SDA), R, is N(16)-methylsparteinium I and is prepared as previously reported. 14 In the absence of lithium, I can form pure-silica or borosilicate SSZ-24. 13,14 Thus, the key to the successful preparation of CIT-5 is both the SDA I and the inclusion of lithium. Further synthetic details are forthcoming. 15 Indexation 16 of the synchrotron powder X-ray diffraction (SPXRD) data from the pure-silica sample of CIT-5 revealed the presence of a small amount of an impurity phase together with the predominant CIT-5 phase. The CIT-5 material indexed in the orthorhombic crystal class with refined lattice constants a = 13.694(2), b = 5.0213(5), and c = 25.4970(3) Å (U = 1753.2 Å 3 ). The lattice constants for the impurity hexagonal phase were found to be a = 13.63 and c = 8.30 Å. The unit cell parameters and scanning electron micrographs helpd to identify the impurity phase as SSZ-24 (International Zeolite Association Code AFI). 17 Systematic absences for the orthorhombic CIT-5 phase indicate body-centering consistent with six possible space groups.The starting model for Rietveld refinement of CIT-5 was obtained by an iterative process of model building, distanceleast squares (DLS) 18 refinement of the atomic positions for the model, and comparison of the simulated powder X-ray pattern (CERIUS 19 ) to the experimental pattern. The model with the closest ma...

Irradiation of fast particles like 1 MeV electrons and 2 MeV protons was made for single crystalline cubic silicon carbide (3C‐SiC) grown epitaxially on Si by chemical vapor deposition in order to introduce point defects in the material. Intrinsic point defects in 3C‐SiC have been characterized by electron spin resonance (ESR), positron annihilation spectroscopy (PAS), Hall and photoluminescence (PL) techniques. The structure and annealing behavior of intrinsic defects, e.g. monovacancies at silicon and carbon sublattice sites, are described based on the results obtained by ESR and PAS. The contributions of such point defects to electrical and optical properties of 3C‐SiC are discussed using the Hall and PL results, with a brief review of published work.

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