2b and 2c suggest that the sulfonate groups of PSDA blocks are attached to the edges and vertices (not on the smooth faces) of the
rhombohedral crystals formed earlier and then the non-interacting PEG block sterically hinders the introduction of the inorganic ions into the crystal lattice on the immediate vicinity of attachment region and also acts as stabilizing moiety [9, 27].
This leads us to conclude that La doping helps to retain
rhombohedral structure.
Note the
rhombohedral crystal ghosts (yellow arrow).
Moreover, these authors noted that "the formation of small clusters of grains following a common orientation may correspond to the early stage of the process that produces the
rhombohedral cleavage as the end result" and that "in this process, phase-contrast imaging shows that the organic component is expelled to the exterior of the developing clusters, suggesting fusion of their crystal lattices into broader units".
During this temperature range the mineral changes its crystalline structure and owns
rhombohedral state.
As mentioned above, the inclusions were present in three different orientations intersecting at 60[degrees]/120[degrees], typical of the six-fold rotational symmetry in the basal plane of the
rhombohedral system.
This would indicate that although it is well known that the particle shape of
rhombohedral GCC and kaolin clay particles differs significantly, in the case of its effect on void volume as determined here, it is minimal at best.
The observation that [Zn.sub.0.90][Ni.sub.0.10]O film is magnetically unsaturated, at maximum magnetic field, can be interpreted in terms of change in lattice spacing due to the secondary
rhombohedral phase of [Zn.sub.1-x][Ni.sub.x]O, and in terms of superexchange interaction.
As 0 [less than or equal to] [delta] [less than or equal to] 0.04, the crystallographic structure of LaMn[O.sub.3+[delta]] is orthorhombic structure (Pbmn, c/[square root of (2)] < a < b) and is strongly Jahn-Teller (JT) distorted; with the S increasing, the structure changes to the slightly JT distorted orthorhombic structure (Pbmn, a [less than or equal to] c/[square root of (2)] < b); when the [delta] > 0.1, it falls into the
rhombohedral structure.
The crystal structure of the prepared material [Ca.sub.3][(B[O.sub.3]).sub.2] can be refined to be
rhombohedral, space group R-3c with lattice parameters a = b = 8.638 [Angstrom] and c = 11.849 [Angstrom].
Lo and Hsieh found cubic [Ga.sub.2]Zn[O.sub.4] spinel and
rhombohedral InGaZn[O.sub.4] phases are identified in the 1100[degrees]C-sintered sample in addition to the as-prepared oxide powder phases of [In.sub.2][O.sub.3], [Ga.sub.2][O.sub.3], and ZnO [11].
On the other hand, the XRD spectra of all the FHA samples calcined at 900[degrees]C, showed the presence of well crystallined hexagonal HA together with [beta]-TCP having
rhombohedral structure (JCPDS file: 09-0169) [10].