Ba2LnFeNb4O15 (Ln = Pr, Nd, Sm and Eu) single crystals were grown from high temperature solution ... more Ba2LnFeNb4O15 (Ln = Pr, Nd, Sm and Eu) single crystals were grown from high temperature solution under controlled atmosphere. Chemical, structural and dielectric characterizations were performed on four crystals with tetragonal tungsten bronze (TTB) structure. The main difference between the four crystals compositions is the proportion of rareearth, as well as vacancies, located in the square site. All crystals displayed an incommensurately modulated structure at room temperature in the paraelectric state. The corresponding basic structures were refined using the P4/mbm space group (R = 0.0274; 0.0416; 0.0328; 0.0357 for Ln = Pr, Nd, Sm and Eu respectively). Examination of the structural parameters confirmed the central role played by square-shaped channels in the crystal-chemistry of these materials. All crystals display a relaxor behaviour with Tm(1MHz) ranging from 110 to 270K. The chemical, 2 structural and physical properties of the crystals are discussed and compared, for the latter, with those of corresponding ceramics.
The room-temperature crystal structure of a new Cu(II) oxyphosphate-a Cu 0.50 II TiO(PO 4)-was de... more The room-temperature crystal structure of a new Cu(II) oxyphosphate-a Cu 0.50 II TiO(PO 4)-was determined from X-ray single crystals diffraction data, in the monoclinic system, space group P2 1 /c. The refinement from 5561 independent reflections lead to the following parameters: a ¼ 7.5612(4)Å , b ¼ 7.0919(4)Å , c ¼ 7.4874(4)Å , b ¼ 122.25(1)1, Z ¼ 4, with the final R ¼ 0.0198, wR ¼ 0.0510. The structure of a Cu 0.50 II TiO(PO 4) can be described as a TiOPO 4 framework constituted by chains of tilted corner-sharing [TiO 6 ] octahedra running parallel to the c-axis and cross linked by phosphate [PO 4 ] tetrahedra, where one-half of octahedral cavities created are occupied by Cu atoms. Ti atoms are displaced from the center of octahedra units in alternating long (2.308 Å) and short (1.722 Å) Ti-O(1) bonds along chains. Such O(1) atoms not linked to P atoms justify the oxyphosphate formulation a Cu 0.50 TiO(PO 4). The divalent cations Cu 2+ occupy a Jahn-Teller distorted octahedron sharing two faces with two [TiO 6 ] octahedra. EPR and optical measurements are in good agreement with structural data. The X-ray diffraction results are supported by Raman and infrared spectroscopy studies that confirmed the existence of the infinite chains-Ti-O-Ti-O-Ti-. a Cu 0.50 TiO(PO 4) shows a Curie-Weiss paramagnetic behavior in the temperature range 4-80 K.
... Maryline Guilloux-Viry received the PhD Degree in Physics from the University of Rennes 1, Re... more ... Maryline Guilloux-Viry received the PhD Degree in Physics from the University of Rennes 1, Rennes, France, in 1991. ... Above 800°C, the XRD data of the films indicate a transformation into a rock-salt type accompanied by the zinc disappearance. ...
Ba2LnFeNb4O15 (Ln = Pr, Nd, Sm and Eu) single crystals were grown from high temperature solution ... more Ba2LnFeNb4O15 (Ln = Pr, Nd, Sm and Eu) single crystals were grown from high temperature solution under controlled atmosphere. Chemical, structural and dielectric characterizations were performed on four crystals with tetragonal tungsten bronze (TTB) structure. The main difference between the four crystals compositions is the proportion of rareearth, as well as vacancies, located in the square site. All crystals displayed an incommensurately modulated structure at room temperature in the paraelectric state. The corresponding basic structures were refined using the P4/mbm space group (R = 0.0274; 0.0416; 0.0328; 0.0357 for Ln = Pr, Nd, Sm and Eu respectively). Examination of the structural parameters confirmed the central role played by square-shaped channels in the crystal-chemistry of these materials. All crystals display a relaxor behaviour with Tm(1MHz) ranging from 110 to 270K. The chemical, 2 structural and physical properties of the crystals are discussed and compared, for the latter, with those of corresponding ceramics.
The room-temperature crystal structure of a new Cu(II) oxyphosphate-a Cu 0.50 II TiO(PO 4)-was de... more The room-temperature crystal structure of a new Cu(II) oxyphosphate-a Cu 0.50 II TiO(PO 4)-was determined from X-ray single crystals diffraction data, in the monoclinic system, space group P2 1 /c. The refinement from 5561 independent reflections lead to the following parameters: a ¼ 7.5612(4)Å , b ¼ 7.0919(4)Å , c ¼ 7.4874(4)Å , b ¼ 122.25(1)1, Z ¼ 4, with the final R ¼ 0.0198, wR ¼ 0.0510. The structure of a Cu 0.50 II TiO(PO 4) can be described as a TiOPO 4 framework constituted by chains of tilted corner-sharing [TiO 6 ] octahedra running parallel to the c-axis and cross linked by phosphate [PO 4 ] tetrahedra, where one-half of octahedral cavities created are occupied by Cu atoms. Ti atoms are displaced from the center of octahedra units in alternating long (2.308 Å) and short (1.722 Å) Ti-O(1) bonds along chains. Such O(1) atoms not linked to P atoms justify the oxyphosphate formulation a Cu 0.50 TiO(PO 4). The divalent cations Cu 2+ occupy a Jahn-Teller distorted octahedron sharing two faces with two [TiO 6 ] octahedra. EPR and optical measurements are in good agreement with structural data. The X-ray diffraction results are supported by Raman and infrared spectroscopy studies that confirmed the existence of the infinite chains-Ti-O-Ti-O-Ti-. a Cu 0.50 TiO(PO 4) shows a Curie-Weiss paramagnetic behavior in the temperature range 4-80 K.
... Maryline Guilloux-Viry received the PhD Degree in Physics from the University of Rennes 1, Re... more ... Maryline Guilloux-Viry received the PhD Degree in Physics from the University of Rennes 1, Rennes, France, in 1991. ... Above 800°C, the XRD data of the films indicate a transformation into a rock-salt type accompanied by the zinc disappearance. ...
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