Sr_1/2Ce_5/14□_1/7WO₄: a new modulated ternary scheelite compound

Abstract

For the first time, a ternary tetragonal scheelite structure tungstate with strontium and cerium cations, (Sr,Ce)WO, was synthesized. As much as 35% Ce could be inserted into the structure, leaving 1\over 7 of the (Sr,Ce) cation sites vacant. Partial ordering of Sr and Ce, with atomic displacements, were shown by high-resolution electron microscopy. Two-dimensional incommensurate modulations occur in this material, in small domains 20 nm in size. The band gap of this compound is significantly lower than the band gap of SrWO and this was related to the distortions of WO and (Sr,Ce)O polyhedra. The band gap value of 3.2 eV makes SrCe□WO a promising candidate for violet luminescence.

Application of the GIXRD Technique to Investigation of Damaged Layers in NaNd(WO_4)-=SUB=-2-=/SUB=- and NaNd(MoO_4)-=SUB=-2-=/SUB=- Ceramics Irradiated with High-Energy Ions

“…Ceramics based on mineral-like compounds [9,10], including those with the structure of the mineral scheelite [11,12], are being studied as promising materials for the immobilization of components of radioactive waste. Isostructured scheelite-like compounds can contain many elements in their composition, the isotopes of which are present in the waste of radiochemical technologies [13,14]. In this paper, two series of ceramic samples NaNd(WO 4 ) 2 (NNW) and NaNd(MoO 4 ) 2 (NNMo) with the structure of the mineral scheelite [15][16][17] were studied.…”

Применение метода GIXRD для исследования нарушенных слоев в керамиках NaNd(WO_4)-=SUB=-2-=/SUB=- и NaNd(MoO_4)-=SUB=-2-=/SUB=-, подвергнутых облучению высокоэнергетическими ионами

“…В качестве перспективных материалов для иммобилизации компонентов радиоактивных отходов исследуются керамики на основе минералоподобных соединений [9,10], в том числе со структурой минерала шеелита [11,12]. Изоструктурные шеелитоподобные соединения могут содержать в своем составе многие элементы, изотопы которых присутствуют в отходах радиохимических технологий [13,14]. В настоящей работе исследованы две серии керамических образцов NaNd(WO 4 ) 2 (NNW) и NaNd(MoO 4 ) 2 (NNMo) со структурой минерала шеелита [15][16][17].…”

New cation deficient scheelites (Sr,Ce)nWO4 (n<1): Structural and optical properties

“…With a rare earth ion RE 3+ as substituting cation, the scheelites can be non deficient (n=1) if A sites are occupied by an alkali ion with a 1 + charge [1,[23][24] and deficient if A sites are occupied by a cation 2 + (this work) [18,[25][26]. Amongst them, scheelite structures with Ce 3+ as RE 3+ are seldom [27][28] because of the relativity instability of this cation in air which can lead to the formation of CeO2 [29].…”

“…In cation deficient scheelites, the cations and the structural vacancies on the A site can be more or less ordered, and incommensurate superstructures can appear [22,27]. The appearance of incommensurate modulations is directly linked to the amount of structural vacancies.…”

“…Previously, a new deficient tetragonal scheelite with a high amount of cerium (35%) was synthesized [27], and the catalytic properties of this phase for the partial oxidation of methane and production of H2 was investigated [12]. The aim of the present work was to synthezise tetragonal strontium cerium scheelites compounds with various cerium contents (from 20% to 50%) in order to study the influence of cerium and structural vacancies on the structure and optical properties of the compounds.…”