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Category: materials – Page 84

Dormant capacity reserve in lithium-ion batteries detected

Lithium iron phosphate is one of the most important materials for batteries in electric cars, stationary energy storage systems and tools. It has a long service life, is comparatively inexpensive and does not tend to spontaneously combust. Energy density is also making progress. However, experts are still puzzled as to why lithium iron phosphate batteries undercut their theoretical electricity storage capacity by up to 25% in practice.

In order to utilize this dormant capacity reserve, it would be crucial to know exactly where and how lithium ions are stored in and released from the during the charging and discharging cycles.

Researchers at Graz University of Technology (TU Graz) have now taken a significant step in this direction. Using transmission electron microscopes, they were able to systematically track the lithium ions as they traveled through the battery material, map their arrangement in the crystal lattice of an iron phosphate cathode with unprecedented resolution and precisely quantify their distribution in the crystal.

Cauchy stress tensor

“the Cauchy stress tensor completely defines the state of stress at a point inside a material in the deformed state”

The Cauchy Stress Tensor.

Imagine you’re holding a rubber band in your hands and stretching it.

The SI base units of both stress tensor and traction vector are newton per square metre (N/m2) or pascal (Pa), corresponding to the stress scalar. The unit vector is dimensionless.

The Cauchy stress tensor obeys the tensor transformation law under a change in the system of coordinates. A graphical representation of this transformation law is the Mohr’s circle for stress.

The Cauchy stress tensor is used for stress analysis of material bodies experiencing small deformations: it is a central concept in the linear theory of elasticity. For large deformations, also called finite deformations, other measures of stress are required, such as the Piola–Kirchhoff stress tensor, the Biot stress tensor, and the Kirchhoff stress tensor.

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Emerging chiral two-dimensional materials

Chirality in extended 2D structures exhibits fundamental differences from molecular-level chirality. This Perspective discusses how local molecular chirality is transmitted and amplified to form distinctive global chirality within ultrathin, single-crystalline 2D materials; it also explores the future challenges and potential of this field.

Defying Temperature Limits: Devil’s Staircase Phenomenon Yields Unexpected Hall Effect Breakthrough

Researchers discovered a significant anomalous Hall effect in the magnetic material SrCo6O11 at temperatures above its magnetic transition, where it exhibits a phenomenon known as the “Spin-Fluctuating Devil’s Staircase.” This observation could revolutionize the design of materials for magneto-thermoelectric conversion, impacting the development of new thermoelectric materials.

Here’s a bit of background: When an electric current flows through a metal sample in a magnetic field, it experiences the Lorentz force. This force generates a voltage perpendicular to the magnetic field and current—a phenomenon referred to as the Hall effect.

In magnetic metals, a similar phenomenon—known as the anomalous Hall effect—may occur independently of an external magnetic field, particularly in ferromagnetic materials wherein electron spins are aligned. Generally, this alignment—and thus the anomalous Hall effect—only manifests below a certain temperature, known as the magnetic transition temperature.

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