Crystal structure of Ba2+-exchanged zeolite Y (FAU), /Ba35.5/ [Si121Al71O384] (Si/Al = 1.70)

Abstract

Experimental detailsSingle crystal X-ray diffraction data were collected at Beamline 4A MXW of Pohang Light Source. The crystal evaluation and data collection were done using l =0.76999 Å radiation with a detector-to-crystal distance of 6.0 cm. Preliminary cell parameters and an orientation matrix were determined from 36 sets of frames collected at scan intervals of 5°with an exposure time of 1 second per frame. The basic scale file was prepared using the program HKL2000 [2]. The reflections were successfully indexed by the automated indexing routine of the DENZO program. The final reflections set was obtained from 72 sets of frames with 5°s cans and an exposure time of 1second per frame. DiscussionZeolites are inorganic crystalline and nanoporous solids with well-defined crystal structures. ion at Ba1' is located at site 1' in the sodalite cavities opposite D6Rs; the Ba 2+ ion was recessed by 1.32 Å into the sodalite cavity from their 3-oygen plane. The Ba1'-O3 distance is 2.69(1) Å, which is almost same with the sum of the radii of Ba 2+ and O 2-, 1.34 +1.32 =2.66 Å [3]. Site 2' position (opposite single 6-rings in the sodalite cage) are occupied by 0.5 Ba 2+ ion. The Ba 2+ ion is shifted by 0.88 Å in to the sodalite cage from its 3-oxygen plane (d(Ba2'-O2) =2.58(2) Å and ∠O2-Ba2'-O2 =109(2)°). The remaining 21 Ba 2+ ions are located at three nonequivalent sites 2 (opposite single 6-rings in the supercage) with occupancies of 1, 13, and 7p er unit cell, respectively. One Ba 2+ ion at Ba2A is strongly bonded to three O2 atoms at 2.47(1) Å,which is alittle shorter than the sum of the radii of Ba 2+ +O 2-.The O2-Ba2A-O2 angle is 116.2(7)°.The 13 and 7Ba 2+ ions at Ba2B and Ba2C position bond three O2 at 2.693 (8)

Процессы Переноса Экситонных Возбуждений И Релаксация В Низкоразмерных Полупроводниковых Гетероструктурах С Квантовыми Ямами

“…В частности, определенный интерес представля-ет конкуренция процессов переноса возбуждений между отдельными элементами низкоразмерной полупровод-никовой структуры (квантовыми ямами, нитями или точками) и процессов излучательной или безызлучатель-ной релаксации возбуждений. Явление переноса энергии между экситонными состояниями в квантовых ямах (КЯ), разделенных широкими туннельно-непрозрачными барьерами, описано в ряде экспериментальных работ -см., например, [1][2][3]. Механизмы, предлагаемые для описания данного явления, различаются, однако ча-ще всего основываются на так называемой модели Фёрстера−Декстера [4][5][6].…”