Find the hidden order in disordered crystals

Researcher at Tokyo Tech have discovered the hidden chemical order of Mo and Nb atoms in a disordered state Ba₇Nb₄moaned₂₀by incorporating advanced techniques, including resonance X-ray diffraction and solid-state nuclear magnetic resonance. This study provides valuable insights into how material properties, such as ionic conduction, can be greatly influenced by their hidden chemical regularities. These results will stimulate significant advances in materials science and engineering.

Determining the exact structure of a crystalline solid is a challenging endeavor. Material properties, such as ion conduction and chemical stability, are greatly influenced by chemical regularities and irregularities (work). However, the techniques scientists usually use to describe unknown crystal structures suffer from serious limitations.

For example, X-ray and neutron diffraction methods are powerful techniques for revealing the positions and arrangements of atoms in a crystal lattice. However, they may be inadequate for distinguishing different atomic species with similar X-ray scattering factors and similar neutron scattering lengths.

To solve this problem, a research team led by Professor Masatomo Yashima of the Tokyo Institute of Technology (Tokyo Tech) in Japan set out to develop a new and more robust approach to analyze the regularities and irregularities in crystals. They combined four different techniques to analyze the crystal structure of the important ionic conductor, Ba₇Nb₄moaned₂₀. “We chose Ba₇Nb₄moaned₂₀ as Ba₇Nb₄moaned₂₀based oxides and related compounds are a new class of materials with attractive properties such as high ionic conduction and high chemical stability,” explained Prof. Yashima. “However, given the two Mo⁶⁺ and N.B⁵⁺ cations have similar scattering strength, all Ba structural analysis₇Nb₄moaned₂₀ up to now has been carried out assuming a complete Mo/Nb breakdown.”

As described in their recent paper published at Nature Communications, the researchers used an approach that combines two experimental techniques, resonant X-ray diffraction (RXRD) and solid-state nuclear magnetic resonance (NMR) aided by computational calculations based on density function theory (DFT). NMR provides direct experimental evidence that Mo atoms occupy only the crystallography M2 sites in Ba₇Nb₄moaned₂₀shows the chemical order of Mo atoms.

Next, the researchers used RXRD to calculate the atomic occupancy factors of Mo and Nb. They found that the atomic occupancy factor of Mo was 0.5 at that point M2 sites but zero on all other sites. interestingly, MSite 2 is close to the oxide-ion conductor, the oxygen-deficient Ba layer₇Nb₄moaned₂₀. This shows that the Mo atom is on MSite 2 has a key role in the high conduction of Ba ions₇Nb₄moaned₂₀. Furthermore, DFT calculations show that Mo ordering stabilizes Mo excess compositions exhibiting high ionic conductivity. The position, occupancy and displacement of proton atoms and oxide ions is also determined by neutron diffraction.

“Our results show that the Mo order influences the material properties of Ba₇Nb₄moaned₂₀,” said Prof. Yashima. “In this respect, our work represents a major advance in our understanding of the correlation between crystal structure and ionic conducting material properties.” Furthermore, in contrast to single crystal X-ray and neutron diffraction, the proposed approach can even be extended to polycrystalline samples and other powders.

Overall, the methodology presented in this study can open new avenues for in-depth analysis of chemical disorder/orderliness in materials. In turn, this could lead to developments in physics, chemistry, and materials science and technology.

Only time will tell what other hidden orders and distractions we’ll encounter!

###

Yashima Research Group

Novel Oxychloride Demonstrates High Stability and Oxide-Ion Conduction through Interstitial Oxygen Sites | Tokyo Technology News

Sparking the Future with New Perovskite-Associated Oxide-ion Conductors | Tokyo Technology News

New Material Based on Ba7Nb4MoO20 with High Oxygen-Ion Conductivity Could Unlock a Sustainable Future | Tokyo Technology News

New High Proton Conductor with Oxygen-Deficient Coating Unlocks a Sustainable Future | Tokyo Technology News

Bypassing bottlenecks—A new class of layered perovskite with high oxygen ion conductivity | Tokyo Technology News

Apatite-Type Material without Interstitial Oxygen Shows High Oxide Ion Conductivity by Overbonding | Tokyo Technology News

About the Tokyo Institute of Technology

Tokyo Tech stands at the forefront of research and higher education as the leading university for science and technology in Japan. Tokyo Tech researchers excel in fields ranging from materials science to biology, computer science, and physics. Founded in 1881, Tokyo Tech hosts over 10,000 undergraduate and graduate students annually, who develop into scientific leaders and some of the most sought-after engineers in the industry. Embodying the Japanese philosophy of “monotsukuri,” which means “technical ingenuity and innovation,” the Tokyo Tech community strives to contribute to society through high-impact research.

https://www.titech.ac.jp/english/