The monoclinic phase of PZT ceramics: Raman and phenomenological theory studies

This work reports on the first Raman detection of the tetragonal to monoclinic phase transition in PZT ceramics near morphotropic phase boundary at low temperatures. The transition is characterized by changes in the frequency of lattice modes with the temperature. The results presented here confirm the previous one recently reported by Noheda et al. using high-resolution synchrotron X-ray powder diffraction technique and dielectric measurements. The stability of the new phase is discussed within the framework of phenomenological Landau-Devonshire Theory.Comment: 6 pages including 4 figures, Latex, submitted to Applied Physics Letter

Conformity to peer pressure in preschool children

Both adults and adolescents often conform their behavior and opinions to peer groups, even when they themselves know better. The current study investigated this phenomenon in 24 groups of 4 children between 4;2 and 4;9 years of age. Children often made their judgments conform to those of 3 peers, who had made obviously erroneous but unanimous public judgments right before them. A follow-up study with 18 groups of 4 children between 4;0 and 4;6 years of age revealed that children did not change their “real” judgment of the situation, but only their public expression of it. Preschool children are subject to peer pressure, indicating sensitivity to peers as a primary social reference group already during the preschool years

Developing a coding system for sulking behavior in young children

Children’s sulking behavior is a salient yet understudied emotional phenomenon. It has been hypothesized to result from hurt feelings, humiliation, and anger, and might thus function as a nonverbal measure in the behavioral studies of these emotions. We conducted three studies that served to develop a comprehensive coding system for children’s sulking behavior. The first study explored sulking features in an online survey that used parental and teacher reports. In an event-based parental diary study, we reevaluated the importance of each feature based on its frequency across episodes of sulking behavior and analyzed the time course of sulking episodes. Finally, we analyzed YouTube videos and demonstrated that the coding system could be reliably applied. We also determined a minimal number of necessary features as a classification threshold. The resulting coding system includes the following features: becoming silent, distancing, turning away, gaze avoidance, crossing arms, lowering head, pouting lips, lowered eyebrows, and, probably, utterances of illegitimate devaluation, and relational distancing. Thus, all varieties of sulking seem to have withdrawal from an ongoing interaction in common

Sulking behavior and the emergence of hurt feelings in young children

When do hurt feelings develop? The emotion of feeling hurt is vital for close relationships because it signals that one has been devalued illegitimately, potentially eliciting guilt and the motivation to repair in the partner. We approached the question of when hurt feelings develop by studying the emergence of sulking behavior as an indicator of hurt feelings. In an online-questionnaire study, parents and teachers hypothesized that children begin to sulk during the first 3 years (N = 125). In a cross-sectional event-based diary study, parents observed their 1- to 8-year-old children (N = 40). We found that the youngest child sulked at 20 months of age and that the probability of sulking was at 50% for a child at 25 months. Finally, we conducted a longitudinal event-based diary study where parents observed their children from 16 months on until they sulked for the first time and, at the longest, until their third birthday (N = 29). We found that the probability of sulking was at 25% at 21 months, at 50% for a child at 24–25 months, and at 75% at 28 months, thus, confirming and specifying the results of studies 1 and 2. These findings indicate that the emotion of hurt feelings emerges mainly during the end of the second and the third year. We discuss the limitations of our approach and why and how the development of hurt feelings in the sense of an appraisal needs to be addressed differently

Plasticity in the structure of visual space

Visual space embodies all visual experiences, yet what determines the topographical structure of visual space remains unclear. Here we test a novel theoretical framework that proposes intrinsic lateral connections in the visual cortex as the mechanism underlying the structure of visual space. The framework suggests that the strength of lateral connections between neurons in the visual cortex shapes the experience of spatial relatedness between locations in the visual field. As such, an increase in lateral connection strength shall lead to an increase in perceived relatedness and a contraction in perceived distance. To test this framework through human psychophysics experiments, we used a Hebbian training protocol in which two-point stimuli were flashed in synchrony at separate locations in the visual field, to strengthen the lateral connections between two separate groups of neurons in the visual cortex. After training, participants experienced a contraction in perceived distance. Intriguingly, the perceptual contraction occurred not only between the two training locations that were linked directly by the changed connections, but also between the outward untrained locations that were linked indirectly through the changed connections. Moreover, the effect of training greatly decreased if the two training locations were too close together or too far apart and went beyond the extent of lateral connections. These findings suggest that a local change in the strength of lateral connections is sufficient to alter the topographical structure of visual spac

Polarization states of polydomain epitaxial Pb(Zr1-xTix)O3 thin films and their dielectric properties

Ferroelectric and dielectric properties of polydomain (twinned) single-crystal Pb(Zr1-xTix)O3 thin films are described with the aid of a nonlinear thermodynamic theory, which has been developed recently for epitaxial ferroelectric films with dense laminar domain structures. For Pb(Zr1-xTix)O3 (PZT) films with compositions x = 0.9, 0.8, 0.7, 0.6, 0.5, and 0.4, the "misfit strain-temperature" phase diagrams are calculated and compared with each other. It is found that the equilibrium diagrams of PZT films with x > 0.7 are similar to the diagram of PbTiO3 films. They consist of only four different stability ranges, which correspond to the paraelectric phase, single-domain tetragonal ferroelectric phase, and two pseudo-tetragonal domain patterns. In contrast, at x = 0.4, 0.5, and 0.6, the equilibrium diagram displays a rich variety of stable polarization states, involving at least one monoclinic polydomain state. Using the developed phase diagrams, the mean out-of-plane polarization of a poled PZT film is calculated as a function of the misfit strain and composition. Theoretical results are compared with the measured remanent polarizations of PZT films grown on SrTiO3. Dependence of the out-of-plane dielectric response of PZT films on the misfit strain in the heterostructure is also reported.Comment: 23 pages, 4 figure

The Structural Complexity of (Bi0.5Na0.5)TiO3-BaTiO3 as Revealed by Raman Spectroscopy

The structural phase diagram of the Pb-free ferroelectric (Na1/2Bi1/2)1-xBaxTiO3 (NBT-BT), x<0.1, has been explored by Raman spectroscopy at temperatures from 10 to 470 K. The data provide clear evidence for a proposed temperature-independent morphotropic phase boundary at x \approx 0.055. However, there is no evidence for a structural phase transition across T \approx 370 K for x > 0.055, where bulk-property anomalies appear to signal a transition to a nonpolar or antiferroelectric phase. The results identify that the phase above 370 K shows short-range ionic displacements that are identical to those in the long-range-ordered phase below 370 K. These conclusions provide a natural interpretation of the weak piezoelectric response in this system and have important implications for the search for Pb-free piezoelectrics.Comment: 21 pages, 5 figure

Aging and path integration skill: Kinesthetic and vestibular contributions to wayfinding

In a triangle completion task designed to assess path integration skill, younger and older adults performed similarly after being led, while blindfolded, along the route segments on foot, which provided both kinesthetic and vestibular information about the outbound path. In contrast, older adults’ performance was impaired, relative to that of younger adults, after they were conveyed, while blindfolded, along the route segments in a wheelchair, which limited them principally to vestibular information. Correlational evidence suggested that cognitive resources were significant factors in accounting for age-related decline in path integration performance