School of Physics, Frontier Institute of Science and Technology, MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter and State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China.
Center for Functional Materials, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, 305-0047 Ibaraki, Japan.
Phys Rev Lett. 2023 Mar 17;130(11):116102. doi: 10.1103/PhysRevLett.130.116102.
Ceramics, often exhibiting important functional properties like piezoelectricity, superconductivity, and magnetism, are usually mechanically brittle at room temperature and even more brittle at low temperature due to their ionic or covalent bonding nature. The brittleness in their working temperature range (mostly from room down to cryogenic temperatures) has been a limiting factor for the usefulness of these ceramics. In this Letter, we report a surprising "low-temperature toughening" phenomenon in a La-doped CaTiO_{3} perovskite ceramic, where a 2.5× increase of fracture toughness K_{IC} from 1.9 to 4.8 MPa m^{1/2} occurs when cooling from above room temperature (323 K) down to a cryogenic temperature of 123 K, the lowest temperature our experiment can reach. In situ microscopic observations in combination with macroscopic characterizations show that this desired but counterintuitive phenomenon stems from a reentrant strain-glass transition, during which nanosized orthorhombic ferroelastic domains gradually emerge from the existing tetragonal ferroelastic matrix. The temperature stability of this unique microstructure and its stress-induced transition into the macroscopic orthorhombic phase provide a low-temperature toughening mechanism over a wide temperature range and explain the observed phenomenon. Our finding may open a way to design tough ceramics with a wide temperature range and shed light on the nature of reentrant transitions in other ferroic systems.
陶瓷通常具有重要的功能特性，如压电性、超导性和磁性，但由于其离子或共价键合的性质，在室温下通常具有机械脆性，在低温下甚至更脆。在其工作温度范围内（主要从室温降至低温）的脆性一直是这些陶瓷实用性的限制因素。在这封信中，我们报告了一种令人惊讶的“低温增韧”现象，即在 La 掺杂的 CaTiO3 钙钛矿陶瓷中，当从室温以上（323 K）冷却到最低可达 123 K 的低温时，断裂韧性 KIC 从 1.9 增加到 4.8 MPa·m1/2 ，增加了 2.5 倍。原位微观观察与宏观特性相结合表明，这种期望但违反直觉的现象源于反向应变玻璃转变，在此期间，纳米尺寸的正交铁弹性畴逐渐从现有的四方铁弹性基体中出现。这种独特微结构的温度稳定性及其对宏观正交相的应力诱导转变为宽温度范围提供了低温增韧机制，并解释了观察到的现象。我们的发现可能为设计具有宽温度范围的坚韧陶瓷开辟了一条道路，并为其他铁电系统中的反向转变的性质提供了线索。
