Etude de niobates et tantalates de metaux de transition bivalents

Synthesis, bulk, and surface characterization of niobium-doped Fe2O3 single crystals

“…This is in complete 6 agreement with the phase diagram for Fe2_xNbx03 ternaries, which indicates an a-Fe203 solid solution of niobium at low concentration, less than 2 + 1% (14). Moreover, t.ernary systems like Fe4Nb209 also crystallize with the corundum structure (15), and this prob~bly accounts for the existence of a solid solution of niobium in the a-Fe203 with conservation of the corundum structure.…”

Single crystal growth of Mn4Nb2O9 and its structure-magnetic coupling

“…An antiferromagnetic (AFM) transition is found at Néel temperature T N ¼ 108.4 K. In contrast to Co 4 Nb 2 O 9 , 7 the AFM order of Mn 4 Nb 2 O 9 single crystal is along c axis and the spin op transition does not occur even with a magnetic eld up to 7 T. A structural phase transition is observed with a-direction shrinkage and c-direction expansion around 110 K, which corresponds exactly to the T N of Mn 4 Nb 2 O 9 . The magnetic structure of our AFM Co 4 Nb 2 O 9 single crystal is different from a collinear arrangement with spin parallel to the trigonal axis as proposed previously by Bertaut et al 3 and resembles the Co 2+ magnetic moments found to be almost lying in the basal plane by Khanh et al 8 But the main difference between the samples, which is responsible for the different easy axis directions, is not clear yet. precisely controlled by adjusting the power of the lamps.…”

“…2 Mn 4 Nb 2 O 9 was rst prepared and studied by Bertaut et al 3 X-ray diffraction (XRD) studies showed that Mn 4 Nb 2 O 9 possesses a trigonal crystal structure (space group P 3c1) with two formula units per cell. The magnetic structure of Mn 4 Nb 2 O 9 has also been reported by Bertaut et al 3 and further conrmed by Schwarz et al with antiparallel inter-chain coupling.…”

“…2 Mn 4 Nb 2 O 9 was rst prepared and studied by Bertaut et al 3 X-ray diffraction (XRD) studies showed that Mn 4 Nb 2 O 9 possesses a trigonal crystal structure (space group P 3c1) with two formula units per cell. The magnetic structure of Mn 4 Nb 2 O 9 has also been reported by Bertaut et al 3 and further conrmed by Schwarz et al with antiparallel inter-chain coupling. The study and conrmation of the magnetoelectric effect in these compounds were conducted by Fischer et al 5 Furthermore, magneto-dielectric effect and magnetic-induced electric polarization were observed in polycrystalline Mn 4 Nb 2 O 9 by Fang et al 6 However, detailed data about the physical properties of the single crystal Mn 4 Nb 2 O 9 are still lacking to further understand this material.…”

Single Crystal Refinement of the Incommensurately Modulated Mn0.55Ta0.45O1.7, an Oxygen Deficient Fluorite Type Compound

“…Compounds in this system with known structures are MnTa 2 O 6 , with the columbite type structure [4], Mn 4 Ta 2 O 9 having a corundum related structure [5] and Mn 11 Ta 4 O 21 [3], whose structure can be described as built up from corundum-type Mn 4 O 8 crystallizes in the space group I4 1 /a, with unit cell parameters a = 11.2728 (2), c = 9.8030(3) A Ê [2]. The second phase, Mn 0.6 Ta 0.4 O 1.65 , has a cubic fluorite average structure with the space group Fm3m, a = 4.9826(3) A Ê , and a total vacancy concentration of 17.5% on the oxygen atom sites.…”