Polymorphism of BaTeMo2O9: A new polar polymorph and the phase transformation

Junjie Zhang, Zhonghan Zhang, Weiguo Zhang, Qingxin Zheng, Youxuan Sun, Chengqian Zhang, Xutang Tao

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A new polar polymorph of BaTeMo2O9, α-BaTeMo2O9, has been synthesized by spontaneous crystallization with molten flux based on the TeO2-MoO3 solvent. The two polymorphous phases of BaTeMo2O9 are referred to as β- and α-BaTeMo2O9 according to their crystallization temperature from high to low. The structure of α-BaTeMo2O9 contains two-dimensional (Te 2Mo4O18)4- anionic layers interleaved with Ba2+ cations. Each anionic layer is composed of Mo4O20 tetramers connected to TeOx (x = 3, 4) polyhedra. The Mo6+ and Te4+ are in asymmetric coordination environments attributable to second-order Jahn-Teller (SOJT) effects. Second-harmonic generation (SHG) measurements using 1064 nm radiation show that α-BaTeMo2O9 is phase-matchable. Polarization measurements indicate that α-BaTeMo2O9 is not ferroelectric, i.e., the polarization is not "switchable". In addition, the powder X-ray patterns of the BaTeMo2O9 samples obtained from solid-state reactions revealed that BaTeMo 2O9 undergoes an irreversible phase transition from β-BaTeMo2O9 to α-BaTeMo2O 9 at ∼570 °C. BaMoO4 is found to lower the energy barrier and stimulate the transformation. Furthermore, structural distortions of both polymorphs were calculated to gain a better understanding of the structure-property relationships. Crystal data: α-BaTeMo2O 9, orthorhombic, space group Pca21 (No. 29), a = 14.8683(2) Å, b = 5.6636(1) Å, c = 17.6849(3) Å, V = 1489.21(4) Å3, and Z = 8.

Original languageEnglish
Pages (from-to)3752-3761
Number of pages10
JournalChemistry of Materials
Issue number16
Publication statusPublished - 2011 Aug 23


  • noncentrosymmetric (NCS)
  • phase transformation
  • polar materials
  • Polymorphism
  • second-order Jahn-Teller (SOJT) effects


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