Crystal engineering regulation achieving inverse temperature symmetry breaking ferroelasticity in a cationic displacement type hybrid perovskite system

Ferroelastic hybrid perovskite materials have been revealed the significance in the applications of switches,sensors,actuators,etc.However,it remains a challenge to design high-temperature ferroelastic to meet the requirements for the practical applications.Herein,we reported an one-dimensional organicinorganic hybrid perovskites(OIHP)(3-methylpyrazolium)CdCl_(3)(3-MBCC),which possesses a mmmF2/m ferroelastic phase transition at 263 K.Moreover,utilizing crystal engineering,we replace-CH_(3) with-NH_(2) and-H,which increases the intermolecular force between organic cations and inorganic frameworks.The phase transition temperature of(3-aminopyrazolium)CdCl_(3)(3-ABCC),and(pyrazolium)CdCl_(3)(BCC)increased by 73 K and 10 K,respectively.Particularly,BCC undergoes an unconventional inverse temperature symmetry breaking(ISTB)ferroelastic phase transition around 273 K.Differently,it transforms from a high symmetry low-temperature paraelastic phase(point group 2/m)to a low symmetry high-temperature ferroelastic phase(point group ī)originating from the rare mechanism of displacement of organic cations phase transition.It means that crystal BCC retains in ferroelastic phase above 273 K until melting point(446 K).Furthermore,characteristic ferroelastic domain patterns on crystal BCC are confirmed with polarized optical microscopy.Our study enriches the molecular mechanism of ferroelastics in the family of organic-inorganic hybrids and opens up a new avenue for exploring high-temperature ferroic materials.

Canonical framework for multi-channel SAR-GMTI

Synthetic aperture radar （SAR） systems have become an important tool for fine-resolution mapping and other remote sensing operations. The multi-channel SAR ground moving-target indication （GMTI） must process its data to produce not only the image of surveillance area but also the information of the ground moving-targets. The topic of moving-target detection in clutter has been extensively studied, and there are many methods that are used to detect moving targets, such as displaced phase center antenna （DPCA） method, along-track interfero-metric （ATI） phase, space-time adaptive processing （STAP）, or some other metrics. A canonical framework is proposed that encompasses all the multi-channel SAR-GMT methods, namely, DPCA and ATI. The statistical test metric for multi-channel SAR-GMTI is established in a simple form, via the definition of the complex central Wishart distribution, to deduce the statistics of the test metric, and the probability distribution of the test metric for multichannel SAR-GMTI has the complex central Wishart distribution of 1×1 case, namely the X^2 distribution. The theory foundation offers the possibility to construct the united multi-channel SAR-GMTI detector, and derives the constant false alarm rate （CFAR） detector tests for separating moving targets from clutter.