Varenik Maxim, Nino Juan Claudio, Wachtel Ellen, Kim Sangtae, Cohen Sidney R, Lubomirsky Igor
Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel.
Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611, United States.
ACS Appl Mater Interfaces. 2021 May 5;13(17):20269-20276. doi: 10.1021/acsami.0c20810. Epub 2021 Apr 22.
The technologically important frequency range for the application of electrostrictors and piezoelectrics is tens of Hz to tens of kHz. Sm- and Gd-doped ceria ceramics, excellent intermediate-temperature ion conductors, have been shown to exhibit very large electrostriction below 1 Hz. Why this is so is still not understood. While optimal design of ceria-based devices requires an in-depth understanding of their mechanical and electromechanical properties, systematic investigation of the influence of dopant size on frequency response is lacking. In this report, the mechanical and electromechanical properties of dense ceria ceramics doped with trivalent lanthanides (RECeO, RE = Lu, Yb, Er, Gd, Sm, and Nd) were investigated. Young's, shear, and bulk moduli were obtained from ultrasound pulse echo measurements. Nanoindentation measurements revealed room-temperature creep in all samples as well as the dependence of Young's modulus on the unloading rate. Both are evidence for viscoelastic behavior, in this case anelasticity. For all samples, within the frequency range = 0.15-150 Hz and electric field ≤ 0.7 MV/m, the longitudinal electrostriction strain coefficient (||) was 10 to 10-fold larger than expected for classical (Newnham) electrostrictors. However, electrostrictive strain in Er-, Gd-, Sm-, and Nd-doped ceramics exhibited marked frequency relaxation, with the Debye-type characteristic relaxation time τ ≤ 1 s, while for the smallest dopants-Lu and Yb-little change in electrostrictive strain was detected over the complete frequency range studied. We find that only the small, less-studied dopants continue to produce useable electrostrictive strain at the higher frequencies. We suggest that this striking difference in frequency response may be explained by postulating that introduction of a dopant induces two types of polarizable elastic dipoles and that the dopant size determines which of the two will be dominant.
对于电致伸缩器和压电材料的应用而言，技术上重要的频率范围是几十赫兹到几十千赫兹。钐和钆掺杂的二氧化铈陶瓷是优异的中温离子导体，已被证明在低于1赫兹时表现出非常大的电致伸缩效应。其原因尚不清楚。虽然基于二氧化铈的器件的优化设计需要深入了解其机械和机电性能，但缺乏对掺杂剂尺寸对频率响应影响的系统研究。在本报告中，研究了掺杂三价镧系元素（RECeO，RE = 镥、镱、铒、钆、钐和钕）的致密二氧化铈陶瓷的机械和机电性能。通过超声脉冲回波测量获得了杨氏模量、剪切模量和体积模量。纳米压痕测量揭示了所有样品在室温下的蠕变以及杨氏模量对卸载速率的依赖性。这两者都是粘弹性行为（在这种情况下为滞弹性）的证据。对于所有样品，在频率范围 = 0.15 - 150赫兹和电场 ≤ 0.7兆伏/米内，纵向电致伸缩应变系数（||）比传统（纽纳姆）电致伸缩器预期的大10到10倍。然而，铒、钆、钐和钕掺杂陶瓷中的电致伸缩应变表现出明显的频率弛豫，德拜型特征弛豫时间τ ≤ 1秒，而对于最小的掺杂剂镥和镱，在所研究的整个频率范围内未检测到电致伸缩应变有明显变化。我们发现只有较小的、研究较少的掺杂剂在较高频率下仍能产生可用的电致伸缩应变。我们认为，频率响应的这种显著差异可以通过假设掺杂剂的引入会诱导两种类型的可极化弹性偶极子，且掺杂剂尺寸决定哪种偶极子占主导来解释。
