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337927 
Journal Article 
Enhanced ordered structure and relaxor behaviour of 0.98Pb(Mg[sup]1/3[/sup]Nb[sup]2/3[/sup])03-0.02La(Mg2/3Nb[sup]1/3[/sup])03 single crystals 
Xifa, L; Bokov, AA; Ye, ZG; Weiguo, QU; Xiaoli, TAN 
2008 
Yes 
Journal of Physics: Condensed Matter
ISSN: 0953-8984
EISSN: 1361-648X 
20 
1 
High quality Pb(Mg[sup]1/3[/sup]Nb[sup]2/3[/sup])O[sup]3[/sup] (PMN) and La-doped PMN (PLMN) single crystals were grown via a top-seeded solution growth method. At a doping level as low as 2 at.% of La, the 1:1 B-site cation (chemical) order was significantly enhanced as revealed by the presence of superlattice peaks in the x-ray diffraction pattern and comparatively large (∼100 nm) chemically ordered regions (CORs) in the transmission electron microscopy dark field images. The average chemical order parameter was calculated (from the intensity of superlattice peaks) to be S ≈ 0.44. Besides, x-ray diffraction revealed the presence of a low-symmetry (presumably rhombohedral) phase. The effect of La doping on the dielectric relaxation was not substantial. Though the magnitude of the dielectric constant peak in PLMN was reduced by half as compared to pure PMN, the peak temperature and diffuseness as well as the shape of the dielectric relaxation spectra remained almost unchanged. The analysis of the temperature dependence of the characteristic time for the main relaxation process in terms of the Vogel-Fulcher law revealed the freezing of dipole dynamics at temperature T[sup]f[/sup] = 192 K, which was only slightly lower than the T[sup]f[/sup] = 213 K in PMN. To reconcile the structural and dielectric data we suggest that the rhombohedral phase forms inside CORs while the chemically disordered matrix remains cubic and is populated by dynamic polar nanoregions that give rise to the characteristic dielectric response. (English) 
Monocristal; Relaxeur; Addition lanthane; Relation structure propriété; Croissance cristalline en solution; Constante diélectrique; Relaxation diélectrique; Paramètre ordre; Microscopie électronique émission champ; Microscopie électronique transmission; Diffraction RX; Dopage; Magnoniobate de plomb; Monocrystals; Relaxor; Lanthanum additions; Property structure relationship; Crystal growth from solutions; Permittivity; Dielectric relaxation; Order parameters; Field emission electron microscopy; Transmission electron microscopy; XRD; Doping; Lead magnesium niobate; Relación estructura propiedad; Niobato de Magnesio y plomo