Room-Temperature Creep Behavior and Activation Volume of Dislocation Nucleation in a LiTaO3 Single Crystal by Nanoindentation

Abstract

The crystal orientation effect on mechanical heterogeneity of LiTaO3 single crystals is well known, whilst the time-dependent plastic behavior, i.e., creep is still short of understanding. Relying on nanoindentation technology, we systematically studied room-temperature creep flows at various holding depths (100 nm to 1100 nm) in three typical orientations namely the X-112°, Y-36° and Y-42° planes. Creep resistance was much stronger in the X-112° plane than the others. In the meanwhile, creep features were similar in the Y-36° and Y-42° planes. The orientation effect on creep deformation was consistent with that on hardness. The nanoindentation length scale played an important role in creep deformation that creep strains were gradually decreased with the holding depth in all the planes. Based on strain rate sensitivity and yield stress, the activation volumes of dislocation nucleation were computed at various nanoindentation depths. The activation volumes ranged from 5 Å3 to 23 Å3 for the Y-36° and Y-42° planes, indicating that a point-like defect could be the source of plastic initiation. In the X-112° plane, the activation volume was between 6 Å3 and 83 Å3. Cooperative migration of several atoms could also be the mechanism of dislocation activation at deep nanoindentation.

On the Room-Temperature Creep Behavior and Its Correlation with Length Scale of a LiTaO3 Single Crystal by Spherical Nanoindentation

“…The pre-existing dislocation density at the onset of the holding stage would change with nanoindentation depth and strain, explaining the variation in SRS. In addition, the estimated SRS values of the Y-42 • plane under spherical tip in plastic holdings were in good agreement with those obtained by Berkovich nanoindentation in the authors' previous work [16]. This further suggests that the nanoindentation creep mechanism of LiTaO 3 is independent of indenter type and size.…”

“…Creep displacement increased from approximately 5 to 90 nm as holding depth increased from 25 to 850 nm. In comparison, the total creep displacements under spherical tips and Berkovich indenter were similar at holding depths ranging approximately from 100 to 600 nm [16]. Figure 3b exhibits the creep rate in the steady-state stage as a function of holding depth.…”

“…Therefore, we can assume that better atomic motion facilitates creep deformation when adopting a smaller spherical tip. On the other hand, the effect of indentation size on hardness has been widely reported in numerous studies [30][31][32], including with respect to LiTaO 3 single crystals [16]. It is widely accepted that a higher density of dislocations or other plastic deformation mechanisms beneath the indenter could be facilitated by reducing the nanoindentation depth.…”

“…Notwithstanding the unavoidable influence of thermal drift, which greatly hinders high-temperature mechanical investigations, nanoindentation has been widely adopted to explore the time-dependent plastic deformation of materials at room temperature [11][12][13][14][15]. In the authors' previous work [16], the room-temperature creep behavior and its correlation with structure orientation of a LiTaO 3 single crystal were revealed by nanoindentation with a standard Berkovich indenter. However, the detailed creep deformations concerned with holding stress, strain and nanoindentation length scale were easily missing under the self-similar Berkovich indenter.…”

Influence of Post-Annealing on the Structural and Nanomechanical Properties of Co Thin Films

“…In addition, it has been widely recognized that the loading and unloading segments of the nanoindentation load-displacement curves often reflect rich information about the dominant deformation mechanism prevailing in the materials under investigation. For instance, the load-displacement responses provide substantial insights into the onset of plastic deformation, phase transformation, creep resistance or fracture behaviors of the various materials [16][17][18][19][20][21][22][23]. In nanoindentation, it has been ubiquitously identified that the materials often exhibit a characteristic feature called the "pop-in" phenomenon during loading.…”