0428同步年報-2021-全

078 ACTIVITY REPORT 2021 temperature and compositional phase diagram were obtained; a new magnetic ordered phase was observed ( Fig. 2 ). the Utilizing web-based symmetry analysis tool, ISODISTORT , 3 the evolution of tetragonality and the transformation of orbital-ordering distortion modes were revealed. At a particular doping region, an arrangement of alternating ordered-insulating and disordered-conducting electron stripes forms a new state of matter. Such structural insight provides evidence showing how an external magnetic field induces the collapse of an insulating state, and how the MR effect might be enhanced in operational temperatures and sensitivities. The collaborative team by using symmetry-analysis approach also demonstrated a new paradigm of improper ferroelectric polarization. In type-II MF mechanism, the polarization is a secondary order parameter of the primary magnetic ordering. Novel HgMn 7 O 12 (HMO) quadruple perovskite was prepared with HPHT techniques, exhibiting a MF property at low temperarture. 4 Compared to its analogue CaMn 7 O 12 , in addition to the charge-ordering phase transition from cubic to rhombohedral phases at high temperature, HMO experienced a further symmetry- lowering transition on cooling at ~260 K to orthorhombic phase Pnn 2 according to SXRD and NPD joint Rietveld refinement ( Fig. 3 ). It was revealed from symmetry element analysis that the improper ferroelectric polarization in HMO originated from the lattice instabilities directly linked to charge and orbital degrees of freedom. In summary, the recent work of Chen and his collaborators demonstrated that the detailed crystallographic information was basic but essential to explain the physical properties intrinsically. The systematic examination of symmetry elements has provided crucial structural insight and mechanistic understanding of intriguing physical phenomena that are not only fascinating in fundamental research but also important in technological application. Collaborative projects adopting symmetry-analysis approach continue to further examine the magnetic structures and commensurate-incommensurate magnetic- phase transitions of the related functional materials. (Reported by Wei-Tin Chen, National Taiwan University) This report features the quadruple perovskite-related work of Wei-Tin Chen and his collaborators published in Nat. Commun. 12 , 6319 (2021) and Phys. Rev. B 97 , 144102 (2018). ANSTO WOMBAT – High-intensity Powder Diffractometer ANSTO ECHIDNA – High-resolution Powder Diffractometer TPS 19A High-resolution Powder X-ray Diffraction • NPD, PXRD • Materials Science, Condensed-matter Physics, Chemistry References 1. M. Uehara, S. Mori, C. H. Chen, S. W. Cheong, Nature 399 , 560 (1999). 2. W.-T. Chen, C.-W. Wang, C.-C. Cheng, Y.-C. Chuang, A. Simonov, N. C. Bristowe, M. S. Senn, Nat. Commun. 12 , 6319 (2021). 3. B. J. Campbell, H. T. Stokes, D. E. Tanner, D. M. Hatch, J. Appl. Crystallogr. 39 , 607 (2006). 4. W.-T. Chen, C.-W. Wang, H.-C. Wu, F.-C. Chou, H.-D. Yang, A. Simonov, M. S. Senn, Phys. Rev. B 97 , 144102 (2018).