Global instability index as a crystallographic stability descriptor of halide and chalcogenide perovskites

Crystallographic stability is an important factor that affects the stability of perovskites.The stability dictates the commercial applications of lead-based organometal halide perovskites.The tolerance factor(t)and octahedral factor(μ)form the state-of-the-art criteria used to evaluate the perovskite crystallographic stability.We studied the crystallographic stabilities of halide and chalcogenide perovskites by exploring an effective alternative descriptor,the global instability index(GII)that was used as an indicator of the stability of perovskite oxides.We particularly focused on determining crystallographic reliability by calculating GII.We analyzed the bond valence models of the 243 halide and chalcogenide perovskites that occupied the lowest-energy cubic-phase structures determined by conducting the first-principles-based total energy minimization calculations.The decomposition energy(ΔHD)reflects the thermodynamic stability of the system and is considered as the benchmark that helps assess the effectiveness of GII in evaluating the crystallographic stability of the systems under study.The results indicated that the accuracy of predicting thermodynamic stability was significantly higher when GII(73.6%)was analyzed compared to the cases when t(55%)andμ(39.1%)were analyzed to determine the stability.The results obtained from the machine learning-based data mining method further indicate that GII is an important descriptor of the stability of the perovskite family.

Assessment of the Internal Instability for Granular Soils Subjected to Seepage

The knowledge of the internal stability of granular soils is a key factor for the design of granular and filter for the geotechnical infrastructures such as dykes, barrages, weirs and roads embankment. To evaluate the internal instability of granular soils different criteria are generally used in the practice. However, the results of these criteria on the same soil may lead to different evaluations of the internal instability. In this paper the common criteria used for the internal instability have been presented and compared as far as possible. It was found that the most internal instability criteria define a limit value for the secant slope of the grain size distribution curve of the granular soils. Based on this finding an own criterion for the evaluation of the internal instability of granular soil has been developed and compared to the common criteria. A very good agreement between some criteria was found. Furthermore, a site specific assessment for the evaluation of the internal instability of granular soil has been proposed in order to get more confidence in this evaluation.

Analysis on Climatic and Synoptic Characteristics of Thunderstorm Gale Weather in Jiangsu

By using observation and sounding data at 68 artificial observatories of Jiangsu Province during 2009- 2013,thunderstorm gale weather and its climatic characteristics in Jiangsu were conducted statistics. The characteristics of some instability indexes and strong convection parameters were analyzed,and environmental parameters of dry and wet thunderstorm gales were contrasted. Results showed that thunderstorm gale in Jiangsu had the characteristics of high occurrence frequency,local feature and stronger intensity. It was mostly accompanied by precipitation,and had obvious seasonal and daily change characteristics. Synoptics analysis showed that temperature-humidity profile characteristics before thunderstorm gale appeared in Jiangsu mainly had four types： bell mouth type,inverted V type,dry unstable type and wet unstable type. Before thunderstorm gale occurred,atmospheric instability was stronger,and some strong convection parameters all had certain instructions. But the forecasts of some thunderstorm gale processes were easy to be missed by only considering CAPE. Environmental condition difference of generating dry and wet thunderstorm gale was that instability of dry thunderstorm gale was stronger than that of wet thunderstorm gale. Before dry thunderstorm gale occurred,environmental temperature at middle-low layer was lower; lapse rate was larger; humidity was small. Before wet thunderstorm gale occurred,environmental temperature was higher; lapse rate was small; humidity was large. At dynamic structure,vertical wind shear at 0- 6 km of dry thunderstorm gale was significantly stronger than that of wet thunderstorm gale.