Defect‐Mediated Anisotropic Lattice Expansion in Ceramics as Evidence for Nonthermal Coupling between Electromagnetic Fields and Matter
Abstract
Electromagnetic (EM) fields can trigger a range of surprising responses in materials. Microwave radiation (MWR), a type of EM field in the frequency range of 0.3–300 GHz, can lower the synthesis temperature required for ceramics such as TiO2 and induces mixed amorphous–crystalline phase compositions. To better understand the effects of MWR on matter, structural changes during microwave heating and MWR‐assisted synthesis using in situ synchrotron X‐ray diffraction are studied. Anisotropic expansion–contraction of lattice parameters under microwave‐radiation is observed, which contradicts the results from conventional thermal heating. When as‐received TiO2 powders are heated with MWR, an instantaneous decrease in the intensities of diffraction peaks indicates decrystallization/amorphization. High‐resolution electron microscopy supports these observations. Raman spectroscopy and X‐ray photoemission spectroscopy indicate increased defect‐generation under microwave exposure. Molecular dynamics simulations on the anatase phase of TiO2 suggests that introducing an oxygen vacancy can lead to the formation of an interstitial–vacancy pair resulting in anisotropic expansion–contraction of the lattice. These unique responses of ceramics under externally applied fields provide direct evidence for nonthermal coupling between EM fields and matter. Understanding such nonthermal, field‐driven processes has implications in engineering low‐temperature processes for integrating ceramics with polymers for flexible electronics, energy harnessing, and storage applications.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Sep 26, 2019
- Source ID
- 10.1002/adem.201900762
Entities
People
- Alan J H McGaughey
- B. Reeja-Jayan
- Haiyan Wang
- Han Wang
- John S Okasinski
- Laisuo Su
- Nathan Nakamura
- Phil M. Smith
- Shikhar Krishn Jha
- Shuyan Zhang
- Xin L. Phuah
Organizations
- Argonne National Laboratory
- Army Research Office
- Carnegie Mellon University
- Office of Naval Research
- Purdue University