#polycrystalline

Artificial intelligence unravels mysteries of polycrystalline materials

Researchers at Nagoya University in Japan have used artificial intelligence to discover a new method for understanding small defects called dislocations in polycrystalline materials, materials widely used in information equipment, solar cells, and electronic devices, that can reduce the efficiency of such devices. The findings were published in the journal Advanced Materials. Almost every device that we use in our modern lives has a polycrystal component. From your smartphone to your computer to the metals and ceramics in your car. Despite this, polycrystalline materials are tough to utilize because of their complex structures. Along with their composition, the performance of a polycrystalline material is affected by its complex microstructure, dislocations, and impurities. A major problem for using polycrystals in industry is the formation of tiny crystal defects caused by stress and temperature changes. These are known as dislocations and can disrupt the regular arrangement of atoms in the lattice, affecting electrical conduction and overall performance. To reduce the chances of failure in devices that use polycrystalline materials, it is important to understand the formation of these dislocations.

Radiation damage simulation software developed for defect accumulation mechanisms study in polycrystalline materials

Recently, the research group led by Prof. Liu Changsong from Institute of Solid State Physics (ISSP), Hefei Institutes of Physical Science (HFIPS) of Chinese Academy of Sciences (CAS) developed a set of software for simulating the evolution of displacement damage in polycrystalline metals at across time and space scales, which was named object kinetic Monte Carlo-lattice kinetic Monte Carlo (OKMC-LKMC) hybridization simulation software.

Using this software, research team explored the accumulation and evolution of vacancies at iron (Fe) grain boundaries (GBs).

The results were published in the Journal of Nuclear Materials.

Polycrystalline/Nanocrystalline (PC/NC) Fe was found to exhibit improved radiation resistance. In previous multiscale simulations, GBs were often abstracted as two-dimensional planes without specific structures, and a series of energetic and kinetic parameters were used to characterize the structural characteristics of GBs.

Generalization of the Hall-Petch and inverse Hall-Petch relations

Most crystalline materials are polycrystals, such as metals. They are composed of many small crystalline grains with different lattice orientations. The interface between two crystalline grains, i.e., the grain boundary, is a thin layer of disordered particles about one or two particles thick.

The polycrystal strength increases as the mean grain size decreases, known as the famous Hall-Petch behavior. This trend reverses when the mean grain diameter is below a critical value of 10–15 nanometers (about 50 atoms), i.e., the reverse Hall-Petch behavior. These trends hold for various polycrystals composed of different atoms and molecules.

However, how the strength varies with the thickness of the disordered grain boundary has rarely been asked and poorly understood, probably because polycrystals with thick grain boundaries are not easy to fabricate and control. Although this basic question can be relatively easily explored by computer simulation, related research remains lacking.

Ultrahigh piezoelectric performance demonstrated in ceramic materials

The ability of piezoelectric materials to convert mechanical energy into electrical energy and vice versa makes them useful for various applications from robotics to communication to sensors. A new design strategy for creating ultrahigh-performing piezoelectric ceramics opens the door to even more beneficial uses for these materials, according to a team of researchers from Penn State and Michigan Technological University.

"For a long time, piezoelectric polycrystalline ceramics have shown limited piezoelectric response in comparison to single crystals," said Shashank Priya, associate vice president for research and professor of materials science and engineering at Penn State and co-author of the study published in the journal Advanced Science. "There are many mechanisms that limit the magnitude of piezoelectricity in polycrystalline ceramic materials. In this paper, we demonstrate a novel mechanism that allows us to enhance the magnitude of the piezoelectric coefficient several times higher than is normally expected for a ceramic."

The piezoelectric coefficient, which describes the level of a material's piezoelectric response, is measured in picocoulombs per Newton.  

Team achieves 30-fold enhancement of thermoelectric performance in polycrystalline tin selenide

The continued depletion of fossil fuel-based energy resources is leading us towards a growing energy crisis. Consequently, this has set in motion a search for sustainable alternative resources. Thermoelectric energy conversion—a process of generating electricity from waste heat—has gained momentum as the next potential energy harvesting technology. Generators made up of thermoelectric materials are used to harvest thermal energy via the "Seebeck effect." The temperature difference in the thermoelectric material creates a flow of charge carriers, generating electrical energy.

For efficient conversion, a thermoelectric material must have a high conversion efficiency (ZT), which needs a high Seebeck coefficient (S), a high electronic conductivity (σ), and a low thermal conductivity (κ). The material tin selenide (SnSe) is known to exhibit a record high ZT in its single crystal form. However, the performance deteriorates in practical polycrystals because of a low σ and a high κ.

In a recent study published in Advanced Science, a team of researchers from Japan, led by Associate Professor Takayoshi Katase from Tokyo Institute of Technology (Tokyo Tech) managed to enhance the ZT of polycrystalline SnSe by demonstrating a high σ and a low κ simultaneously. The team achieved this remarkable breakthrough by introducing tellurium (Te) ion into the structure of SnSe.

Engineers model nanoscale crystal dynamics in easy-to-view system

Rice University engineers who mimic atom-scale processes to make them big enough to see have modeled how shear influences grain boundaries in polycrystalline materials.

That the boundaries can change so readily was not entirely a surprise to the researchers, who used spinning arrays of magnetic particles to view what they suspect happens at the interface between misaligned crystal domains.

According to Sibani Lisa Biswal, a professor of chemical and biomolecular engineering at Rice's George R. Brown School of Engineering, and graduate student and lead author Dana Lobmeyer, interfacial shear at the crystal-void boundary can indeed drive how microstructures evolve.

The technique reported in Science Advances could help engineers design new and improved materials.