Grain boundary stabilization of ultrathin ferroelectric ZrO₂ films

 

Grain boundaries (GBs) are ubiquitous topological defects in polycrystalline materials that play a crucial role in determining their macroscopic properties, such as mechanical strength, radiation tolerance, and thermal conductivity. For example, dense networks of GBs hinder dislocation motion, thereby hardening and strengthening nanostructured metals and superhard materials.

Defect engineering and microstructural modification have traditionally treated GBs simply as auxiliary elements for tuning material properties. However, recent studies suggest that GBs not only act as secondary regulators but also as independent heterointerfaces capable of stabilizing grain phase structures and inducing emergent functionalities.

The possibility of controlling crystalline phases through GB manipulation gained relevance with the discovery of ferroelectricity in nanocrystalline fluorite-based films of HfO₂ and ZrO₂, where ferroelectricity arises in a metastable, non-centrosymmetric orthorhombic (O) phase. However, the role of GBs in stabilizing the O-phase at the nanoscale has been scarcely explored, partly due to the difficulty of accurately determining their atomic-scale structure and chemical composition.

A group of researchers in China succeeded in growing, by chemical methods, an ordered La(Sr)–Mn–O superstructure exclusively at the GBs of ultrathin polycrystalline ZrO₂ films (with thicknesses below 5 nm), which stabilizes the metastable ferroelectric O-phase. The atomic configurations of the La(Sr)–Mn–O superstructure and its ordered growth were identified using atomic-resolution imaging and electron energy loss spectroscopy (EELS). Charge distribution and Mn–O electronic interactions were confirmed using four-dimensional scanning transmission electron microscopy (4D-STEM). First-principles calculations demonstrate an ordered arrangement of the eg/t2g orbitals of Mn³⁺/Mn⁴⁺ ions along the GBs. This arrangement induces alternating interactions with oxygen ions, periodically modulating the strength of Zr–O bonds and ultimately stabilizing the ferroelectric state on both sides of the GBs.

These findings propose a stabilization mechanism for metastable polar phases through a novel grain boundary chemistry, opening pathways toward ultra-stable nanoelectronics.

For further information go to: Nature Materials

Practical lithium–organic batteries enabled by an n-type conducting polymer

 

Currently, the widespread use of portable electronic devices demands batteries with higher storage capacities and longer lifetimes. Among the various options available on the market, lithium-ion batteries (LIBs) stand out due to their high energy storage capacity and long service life. However, these devices are typically composed of inorganic materials derived from limited mineral resources, which leads to negative environmental impacts. For this reason, research efforts have been directed toward finding more sustainable and environmentally friendly alternatives.

Scientists from several Chinese universities have developed organic lithium batteries using an n-type conductive polymer, poly(benzodifurandione) (PBFDO). PBFDO exhibits excellent ionic and electronic transport properties, high electrical conductivity (>2000 S/cm), low solubility in liquid electrolytes, and thermal structural stability up to 200 °C. The researchers constructed polymer cathodes with an ultrahigh mass loading of up to 206 mg/cm², achieving a specific capacity of 42 mAh/cm². In addition, 2.5 Ah lithium-organic pouch cells were fabricated with an energy density of 255 Wh/kg, comparable to that of commercial lithium-ion batteries.

The results reveal π–π stacking of the (010) planes with interplanar distances of 0.34 nm and lamellar stacking of the (100) planes with interplanar distances of 1.04 nm. Within these stacked structures, channels containing a large number of carbonyl groups are formed, which are attributed to enabling efficient lithium transport. These cells demonstrated strong cycling stability, resistance to nail penetration without explosion or fire, and efficient performance across an extreme temperature range (−70 °C to 80 °C). The flexibility of the PBFDO cathodes was also highlighted, making them suitable for applications in portable electronics. Furthermore, the energy storage mechanism of PBFDO was investigated, showing that carbonyl groups act as active sites for lithium-ion storage.

This work opens the door to the use of n-type conductive polymers as electrodes in LIBs, since the type of charge carriers (electrons) helps maintain charge balance when Li⁺ is inserted into the electrode, in contrast to p-type conductive polymers whose charge carriers (holes) make charge balance more difficult.

More information at: NATURE

Consolidating mural plaster layer with nanolime

 

Treatment of the mural plaster layer with NL. a) Spraying of NL dispersion on the surface of the mural plaster layer. b) Spraying deionized water onto the surface after 10 min the application of the NL dispersion. c) Mural plaster layer, with NL applied for consolidation in samples 1, 2, and 3. d) Mural plaster layer after consolidation. e), f), g) Samples 1, 2, and 3 before consolidation, respectively. h), i), j) Samples 1, 2, and 3 after consolidation, respectively. k) Mural pigment layer of samples 1, 2, and 3.

The pigment of many ancient mural paintings rests on a layer of lime and clay known as plaster, which deteriorates with aging, leading to a decrease in its mechanical strength. A team of researchers from China and Spain studied methods to strengthen the plaster layer using lime nanoparticles or nanolime (NL), a dispersion of calcium hydroxide nanoparticles. NL overcomes the limitations of other consolidants, such as organic materials or acrylic resins, which reduce the breathability of the material and, over time, generate new aging-related problems.

The researchers developed a synthesis procedure to produce NL with uniform size and morphology by using different additives, ultrasonic treatment, and centrifugation. As a result, they obtained nanoparticles of approximately 40 nm in diameter—significantly smaller than the 180 nm obtained without centrifugation. A dispersion of nanolime in ethanol was sprayed with an atomizer onto the plaster layers of fragments from a Chinese mural painting, which were later sprayed with water to accelerate the consolidation of the plaster.

The results showed that the selected nanolime penetrated to a depth of 1.2–3.5 mm, and the surface hardness of the layer increased by approximately 56%. Porosity decreased only minimally (around 5.9%); a slight shift toward smaller pores was observed, indicating effective filling of the structure. Microstructural analysis confirmed the densification of the surface layers after consolidation. No whitening of the pigment layer on the surface of the plaster was observed.

The authors concluded that the nanoparticle-sized selected NL provides high-quality consolidation of mural painting plaster and may serve as a methodological alternative for broader application in the conservation of cultural heritage, including murals detached from their original support and preserved in museums.

For further information go to: JOURNAL OF CULTURAL HERITAGE