A propos de la ferroeléctricité dans BaAl2O4

Reduction from Eu3+ to Eu2+ in BaAl2O4:Eu phosphor prepared in an oxidizing atmosphere and luminescent properties of BaAl2O4:Eu

“…1). At room temperature, BaAl 2 O 4 is hexagonal P6 3 and has a superstructure with unit cell parameters 2A, C, where A and C are the lattice parameters of hexagonal tridymite [17][18][19]. Fig.…”

“…Identification of crystalline phase of the samples BaAl 2 O 4 belongs to the large family of stuffed tridymite structures which are derived from the structure of SiO 2 b tridymite [17][18][19]. As Al 3+ replaces Si 4+ in the tetrahedra of SiO 2 tridymite, Ba will occupy sites in channels parallel to the c-axis (see the projection of BaAl 2 O 4 shown in Fig.…”

“…air or pure O 2 gas [3][4][5][6][7][8]. Though this last case is only applicable for a few special compounds with rigid three-dimensional (3-D) enclosed crystal structures, such as sulfates (BaSO 4 :Eu), phosphates (Ba 3 (PO 4 ) 2 :Eu), borophosphates (MBPO 5 [17][18][19][20][21], which exhibits the reduction from Eu 3+ to Eu 2+ when prepared in air [7], the similar phenomenon in BaAl 2 O 4 :Eu is anticipated and further confirmed by this work.…”

Giant thermal vibrations in the framework compoundsBa1−xSrxAl2O4

“…This compound undergoes a structural phase transition from a high-temperature phase with a space group of P 6 3 22 to a low-temperature phase with P 6 3 at approximately 450 K. [10][11][12] This transition is accompanied by the significant tilting of the Al-O-Al bond angle along the c-axis, giving rise to the enlargement of the cell volume to 2a × 2b × c. The crystal structures of the hightemperature and low-temperature phases are shown in Figs. 1(a) and (b), respectively.…”

Magnetoelectric and multiferroic properties of ternary copper chalcogenides Cu2MIIMIVS4

“…The crystal structure of the other materials is just a calculated one as reported in the inorganic crystal structure database [15]. For BaAl 2 O 4 , the ionic model gives an overestimation of P s by a factor of six compared to the experimental value [24]. Sulfur is a softer Lewis base than oxygen, and covalency effects are more dominant than for oxides.…”