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Ferroelectricity in Ternary (CdZn)AVI Crystals
T. Wojciechowski,,P. Jakubas,P. Bogus lawski,G. Karczewski 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.1
Molecular-beam-epitaxy grown thin lms and bulk crystals of Cd1-xZnxTe have been sudied by using various experimental methods. The samples exhibit bistable conductivity, peculiar optical properties and hysteresis in the dielectric constant. The experimental results indicate that the presence of isolated Zn atoms plays a crucial role in the ferroelectric behavior of Cd1-xZnxTe. Based on the experimental results, we propose a microscopic model that takes into consideration formation of point defects in the crystal lattice, namely Zn interstitials, ZnI and cation vacancies, VCd. The presence of these defects and the formation of vacancy-interstitial pairs that constitute local electric dipoles provide a plausible explanation for the bistable conductivity, the changes in the luminescence spectra and of the hysteretic behavior of the electrical polarization. Molecular-beam-epitaxy grown thin lms and bulk crystals of Cd1-xZnxTe have been sudied by using various experimental methods. The samples exhibit bistable conductivity, peculiar optical properties and hysteresis in the dielectric constant. The experimental results indicate that the presence of isolated Zn atoms plays a crucial role in the ferroelectric behavior of Cd1-xZnxTe. Based on the experimental results, we propose a microscopic model that takes into consideration formation of point defects in the crystal lattice, namely Zn interstitials, ZnI and cation vacancies, VCd. The presence of these defects and the formation of vacancy-interstitial pairs that constitute local electric dipoles provide a plausible explanation for the bistable conductivity, the changes in the luminescence spectra and of the hysteretic behavior of the electrical polarization.
Gallagher, S.J.,Reuning, L.,Himmler, T.,Henderiks, J.,De Vleeschouwer, D.,Groeneveld, J.,Rastegar Lari, A.,Fulthorpe, C.S.,Bogus, K.,Renema, W.,McGregor, H.V.,Kominz, M.A.,Auer, G.,Baranwal, S.,Casta& Elsevier 2018 Quaternary science reviews Vol.200 No.-
<P><B>Abstract</B></P> <P>Marine ooids are iconic indicators of shallow seawater carbonate saturation state, and their formation has traditionally been ascribed to physicochemical processes. The Indo-Pacific stands out as a region devoid of oolites, particularly during the Quaternary: the “ooid enigma”. Here we present results from recent coring by the International Ocean Discovery Program (IODP Expedition 356) off west Australia that shows that ooid horizons are common in Pleistocene strata up to 730,000 years old. Extensive “ooid factories” were created due to the presence of long-lived tidally influenced flat–topped tropical platforms suitable for intermittent ooid accretion over hundreds to thousands of years during highstands and times of lower sea level. This work suggests marine ooids may actually be more common in Indo-Pacific than previously reported. Past global ocean alkalinity was elevated during Pleistocene glacial periods and continental climate was generally more arid in the Indo-Pacific region compared to interglacials and the Holocene. Therefore, increased aridity associated with higher alkalinity conditions during the glacials facilitated ooid precipitation on adjacent tropical carbonate platforms particularly offshore from arid Australia. This confluence of factors suggests that more “ooid factories” may be encountered by further coring Indo-Pacific regions with Pleistocene flat long-lived carbonate shelves. However, Indo-Pacific Quaternary ooid occurrences outside Australia are rare, suggesting that the Northwest Shelf may be a unique archive of this non-skeletal precipitate. Further investigations into the petrography and geochemistry of pre-Holocene ooid occurrences will provide insights into their origin and the relative role of biotic, physicochemical and other factors in their formation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Oolites are rare in the Indo-Pacific, particularly during the Quaternary: the “ooid enigma”. </LI> <LI> IODP Expedition 356 off west Australia cored common ooid horizons in strata up to 730,000 years old. </LI> <LI> Extensive “ooid factories” were deposited on tidally influenced flat–topped tropical platforms. </LI> <LI> Oolites were deposited during low and high sea levels in generally arid conditions. </LI> <LI> More “ooid factories” may be found by coring regions with flat long-lived carbonate shelves. </LI> </UL> </P>