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Strong piezoelectricity in the perovskite-type PbZr1−xTixO3 (PZT) and Pb(Zn 1/3 Nb 2/3 )O3-PbTiO3 (PZN-PT) systems is generally associated with the existence of a morphotropic phase boundary (MPB) separating regions with rhombohedral and tetragonal symmetry. An x-ray study of PZN-9%PT has revealed the presence of a new orthorhombic phase at the MPB, and a nearvertical boundary between the rhombohedral and orthorhombic phases, similar to that found for PZT between the rhombohedral and monoclinic phases. We discuss the results in the light of a recent theoretical paper by Vanderbilt and Cohen, which attributes these low-symmetry phases to the high anharmonicity in these oxide systems. Key words: Piezoelectricity, PZN-PT, morphotropic phase boundary, monoclinic perovskite.Ferroelectric perovskite-type materials are of great fundamental and technological importance. Among such materials, the PZT and PZN-PT systems exhibit unusually large piezoelectric coefficients; in particular, extraordinarily high values have recently been reported for PZN-PT by Park and Shrout when an electric field is applied along the pseudocubic [001] direction [1], with d 33 > 2500pC/N and strain values up to 1.7 %. These properties are an order-of-magnitude superior to those of PZT ceramics, currently the materials of choice for a wide variety of high-performance electromechanical devices, and make PZN-PT a promising candidate for a new generation of such devices [2]. In both PZT and PZN-PT, the high piezoelectric coefficients have been associated with an MPB which separates regions having tetragonal (T) and rhombohedral (R) symmetry . However, the recent discovery of a new monoclinic phase in PZT at the MPB has changed this picture dramatically [3][4][5][6][7].The phase diagrams for the two systems are shown in Fig. 1 [ 8,9], with the respective MPB's represented as heavy lines and the recently-discovered monoclinic structure in PZT [3] as M A . A key feature of this new structure is that the polarization vector is no longer constrained to lie along a symmetry axis, as in the rhombohedral (R) and tetragonal (T) structures, but instead can rotate within the monoclinic plane [4][5][6].In the present paper, we report the results of a highresolution synchrotron x-ray powder diffraction study of a sample doped with 9%PT. This study complements single-crystal investigations of 4.5% and 8% PT samples carried out in collaboration with the Penn State group which will be reported elsewhere. In particular, measurements made on rhombohedral 8%PT samples under an electric field have shown that an orthorhombic phase is irreversibly induced by the field, indicative of the close proximity of a rhombohedral-orthorhombic boundary in the phase diagram [10]. The presence of some lowersymmetry phase at room temperature was also revealed in a previous optical study of 9%PT [11], and the present x-ray results show conclusively the presence of this new phase in the PZN-PT phase diagram, which, in contrast to the case of PZT, has orthorhombic rather than monoclin...

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Behavioral rhythms synchronize between humans for communication; however, the relationship of brain rhythm synchronization during speech rhythm synchronization between individuals remains unclear. Here, we conducted alternating speech tasks in which two subjects alternately pronounced letters of the alphabet during hyperscanning electroencephalography. Twenty pairs of subjects performed the task before and after each subject individually performed the task with a machine that pronounced letters at almost constant intervals. Speech rhythms were more likely to become synchronized in human–human tasks than human–machine tasks. Moreover, theta/alpha (6–12 Hz) amplitudes synchronized in the same temporal and lateral-parietal regions in each pair. Behavioral and inter-brain synchronizations were enhanced after human–machine tasks. These results indicate that inter-brain synchronizations are tightly linked to speech synchronizations between subjects. Furthermore, theta/alpha inter-brain synchronizations were also found in subjects while they observed human–machine tasks, which suggests that the inter-brain synchronization might reflect empathy for others' speech rhythms.