Double-perovskite phase

Further, In order to achieve pure double perovskite phases, the precursor samples were put into 2.45 GHz, 6 kW continuously adjustable microwave equipment (HAMiLab-HV3, Syno-Therm), the maximum operating temperature up to 1400°C, and 0.5-3 kW. The multimode... 

A technology of Sr2FeMoObui (SFMO) nanosized films deposition by ion-beam sputtering is described. Optimization of deposition conditions on formation of structural ly-perfect SFMO double perovskite films is presented. Several problems arise with the use of the ion-beam sputtering method concerning the films inhomogeneity, the presence of multiple phases and Femo and Mope antistructural defects. It is shown that they are solved by means of complex selection of parameters substrate temperature, deposition rate and subsequent thermal processing. 

The crystallinity of MW04 (M=Ba, Pb) thin films was studied by IR spectroscopy.223 High-pressure Raman spectra of A12(W04)3 showed phase transitions at 0.28 0.07 and 2.8 0.1 GPa.224 The IR spectrum of the double perovskite Sr2FeW06 includes characteristic bands at 143, 227, 377 and 625 cm-1.225... 

Table 2.1 Phases with the rock-salt-type double perovskite structure...

Bond valence sums are often calculated for these phases to clarify aspects of valence and stmcture - for example, bond valence sums for the double perovskite Ca MgOsOg are Ca—O, 2.03 Mg—O, 2.15 and Os—O, 6.49. These suggest that assigning the ionic states Mg and Ca is reasonable, but the Os cation is significantly overbonded, suggesting that there may be a considerable departure from the formal Os state in the OsO. units. 

In the unusual double perovskite CaMnTi Og, the Mtf cations occupy the A-sites. The Mn + and Ca are ordered in columns along the c-axis, with structural distortions allowing the Mn " to take tetrahedral and square planar positions in the cage sites. The phase CaFeTi Og appears to be similar, but with Fe only occupying tetrahedral positions. These phases are structurally related to the AA B Oj -related phases described in the following section. 

Fig. 7.1 The charged-oidered (CO) phase of the oxygen-deficient double perovskite YBaFe205 (top) orthorhombic unit cell with a chain of alternating Fe d" and Fe + ions along the a direction (bottom) the local coordination of the two iron sites giving the neatest neighbor distances as optimized by a GGA-FU calculation...

SrTiOs is an archetype of the cubic form. A layered structure is obtained for the composition Sr3Ti207, which is built upon blocks of double perovskite slabs shifted to make SrO layers in between [7]. Another structure, Sr4Ti30io, exists with three perovskite slabs [8]. In general, these Ruddlesden-Popper phases can be described with the general formula A2[A iB 03 +i], where n is the thickness of the perovskite slabs (Figure 8.4). The = 1 member also refers to the K2Nip4 structure. 

Figure 2.33 A phase diagram indicating the range of stability of B-site ordered double perovskites, denoted as -I—I—I—I—I- rock salt, in terms of differences in ionic radii and formal charge. Reprinted with permission from Anderson eta/., 1993 [80], Copyright (1993) Elsevier...

On the other hand, to explain the magnetisation and a reduced Ms in n-type metallic double perovskite system, Sr2 xCaa FeMo06 (0 < x < 2), Goodenough and Dass invoked the idea of anti-phase boundaries (APB). 

While an ordered sample ( 91%) of Sr2FeMo06 showed a sharp low-field MR response, it was much lower in a partially disordered ( 31%) sampleJ Therefore, its absence in the disordered phase indicates the obliteration of HMF property due to large AS disor-der. Thus, ordering in double perovskite is crucial for the true nature of the half-metallic ground state and the intrinsic properties of the material. 

The phase structure of the microwave sintered LNMO and LCMO nanoparticles was characterized by X-ray diffraction (XRD). As shown in Figure 4, no extra reflection peaks other than those of pure perovskite phase are detected, indicating the high purity of nanoparticles can be obtained in 10 min by this microwave sintering approach, which confirms the formation of single phase compositions of LNMO and LCMO double perovskites [30]. 

Qian Y, Wu H, Kan E, Lu J, Lu R, Liu Y, Tan W, Xiao C, Deng K. Biaxial strain effect on the electronic and magnetic phase transitions in double perovskite La2peMn06 a first-principles study. Journal of Applied Physics 2013 114 063713. 

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