Development of the BaO-Mg(Zn) O-Ta_2O_5 ternary phase diagram for single crystal growth of the Ba(Mg_<1/3> Ta_<2/3>) O_3 and Ba(Zn_<1/3> Ta_<2/3>) O_3 using off-stoichiometric composition method

本文研究了BaO-MgO（ZnO）-Ta_2O_5系统在1450℃平衡时的相关系。在BaO-MgO-Ta_2O_5系统中发现了与钨青铜结构密切相关的三个三元相：3：1：1钙钛矿型Ba_3MgTa_2O_9、9：1：7 TTB型<14>Ba_9MgTa_O_3<45>和4：1：<10>5Ba_4MgTa_O_4<30>。在1600℃平衡后才能得到具有10层六方钙钛矿结构的三元相Ba_（10）Mg_（0.25）Ta_（7.9）O_（30）。<14>Ba_9MgTa_O_5<45>相具有量子铁电性质，我们还澄清了BaO-MgO-Ta_2O_5组成领域中有关三元相和二元相的一些相互矛盾的报道。例如，我们没有发现<20><63>R. S. Roth[“实验陶瓷系统的相平衡”，NIST项目报告，报告编号1，合同编号SB 1341 -02-W-0787，国家标准与技术研究所陶瓷部;盖瑟斯堡，马里兰州; 2页。（2003）]，也不能证实Ba_7Ta_6O_2相的存在<22>[J. S.金，J. - W.金角，澳-地I. Cheon，Y.- S. Kim，S. Nahm，J. D. Byun，J. Eur.陶瓷。索科，2001，21，2599 ; C.- M.郑玉- T. Hseih，C. F.杨，陶瓷。内部：2002，28，255 ; X. M. Chen，Y. Suzuki，N.佐藤，J.脱线。科学：电子材料，1994，5，244]。TTB型Ba_9MgTa_<14>O_<45>3是沿着BaTa_2O_6形成的。加入Ba 3 MgTa 2 O 9。发现在Mg_4Ta_2O_9-BaTa_2O_6系中，只有沿着六方晶系的BaTa_2O_6相存在，而在BaO-ZnO-Ta_2O_5系中，不能确定Ba_4ZnTa_ O<10>_2<30>化合物的存在。在<24>ZnTa_2O_6-BaTa_2O_6的连接线上发现了沿着的Ba_3ZnTa_8O_2相。用单晶结构分析证明了<24>Ba_3ZnTa_8O_2与Ba_4MgTa_O_2具有等型性<10><30>，并讨论了它们化学成分不同的原因。

We completed investigation of the phase relation in the BaO-MgO(ZnO)-Ta_2O_5 system equilibrated at 1450℃. In the BaO-MgO-Ta2O5 system we found three ternary phases, namely 3:1:1 perovskite Ba_3MgTa_2O_9, 9:1:7 TTB(tetragonal tungsten bronze)-type Ba_9MgTa_<14> O_<45> and 4:1:5 Ba_4MgTa_<10> O_<30> with close relation to the tungsten bronze structure. Another ternary phase, Ba10Mg0.25Ta7.9O30, with 10 layer hexagonal perovskite structure can be only obtained after equilibration at 1600℃. The Ba_9MgTa_<14> O_<45> phase shows quantum ferroelectric properties.We have also clarified several contradictory reports related to the ternary and binary phases in the BaO-MgO-Ta_2O_5 composition field. For example, we found no evidence of the hexagonal Ba_9Mg_4Ta_<20> O_<63> phase that was claimed by R. S. Roth[` Phase Equilibria of Experimental Ceramic Systems', NIST Project Report, Report No.1, Contract No.SB1341-02-W-0787, National Institute of Standards and Technology, Ceramics Division ; Gaithersburg, Maryland ; 2 pp.(2003)], nor we can confirm the existence of the Ba_7Ta_6O_<22> phase reported by several authors[J. S. Kim, J.-W. Kim, C. I. Cheon, Y.-S. Kim, S. Nahm, J. D. Byun, J. Eur. Ceram. Soc., 2001, 21, 2599 ; C.-M. Cheng, Y.-T. Hseih, C.-F. Yang, Ceram. Int., 2002, 28, 255 ; X. M. Chen, Y. Suzuki, N. Sato, J. Mater. Sci.: Materials in Electronics, 1994, 5, 244]. The TTB type Ba_9MgTa_<14> O_<45> forms along the BaTa_2O_6. Ba3MgTa2O9 join. We found that only hexagonal polymorph of the BaTa_2O_6 phase exists along the Mg_4Ta_2O_9-BaTa_2O_6 tie line.In the BaO-ZnO-Ta_2O_5 system we could not confirm the existence of the Ba_4ZnTa_<10> O_<30> compound. Instead, a Ba_3ZnTa_8O_<24> phase has been found along the ZnTa_2O_6-BaTa_2O_6 tie line. Using single crystal structural analysis we have demonstrated that the Ba_3ZnTa_8O_<24> phase is isotypical with the Ba_4MgTa_<10> O_<30> phase and discussed the reasons for the difference in the chemical composition of these phases.