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Heat treatments in air and in vacuum have been performed on crystal and powder of the natural tantalite (Mn2+0.88Fe2+0.09)(Ta5+0.86Nb5+0.14)2O2-6, as well as on powder of synthetic Fe2+(Nb5+0.6Ta5+0.4)2O6. Crystal parameters and hyperfine interactions were obtained by use of x-ray diffraction and Mossbauer spectroscopy. It is shown that the partially ordered natural sample is completely ordered after heat treatment in vacuum. Conversely, heat treatment in air induced the tantalite [(Mn2+0.88Fe2+0.09)(Ta5+0.86Nb5+0.14)2O2-6]wodginite [(Mn2+,Fe2+)Fe3+(Ta,Nb)2O8] transformation on the powdered sample. When applied to the crystal sample, the heat treatment in air produced a mixture of two phases: the one in large amount is the ordered (Mn2+0.88Fe2+0.09)(Ta5+0.86Nb0.145+)2O62-, the other, in minor amount, is (Mn2+0.88,Fe2+0.09)Fe3+(Ta,Nb)2O8. The former arrives from cation ordering in the bulk portion of the sample, while the latter results from the near-surface oxidation. The Mn content as well as the oxidant atmosphere appears to play an important role in the transition mechanism. The same heat treatment applied to the synthetic columbite induces a different reaction: ferrocolumbite is transformed into the ixiolite Fe3+(Nb0.6Ta0.4)O4 with a minor amount of (Nb,Ta)2O5.

Ferroelectric strontium bismuth tantalite (SBT) thin films were fabricated on substrates using pulsed laser deposition combined with an annealing process. The crystallization and ferroelectric properties were clearly dependent on the annealing conditions. SBT thin films with good crystallization and ferroelectric properties were obtained after annealing at for 90 min. The films showed high (115) and (008) diffraction peaks. Good ferroelectric properties were obtained from the films; remnant polarization and coercive field were about and , respectively. No fatigue was observed up to switching cycles. The dc leakage current was about and the dc breakdown field was .

A sample of mineral obtained in the department of Vichada was characterized by the technique of X-ray diffraction in powder samples, in order to determine the crystallographic phases present. After analyzing diffraction patterns, as a result, the mineral had inclusions of Rutile (86.3%) and Manganocolumbita (13.7%). Next, a simulation of the crystal structure of these minerals from the data entered in the databases was carried on. Later, the Rietveld method was used, from this refinement, the new diffraction pattern and the new network parameters were obtained. For the Rutile it was obtained a tetragonal structure, and for the Manganocolumbita an orthorhombic structure was obtained. The characterization is justified among other aspects due to the important applications of these materials in industry and technology, such as Rutile is used in welding rod coatings, in Industries cardboard paper and ink impression among many other uses, the Manganocolumbita is used in special alloys resistant to high temperatures, it also is directly related to the tantalite in coltan formation.

The crystal surface properties of potassium tantalite niobate, KTa0.5Nb0.5O3 (KTN), are studied with first-principles calculation based on the density functional theory (DFT). Generalized gradient approximation (GGA) functional analysis is also employed by using CASTEP software. The explanations for the differences of the ferroelectric and piezoelectric properties between the bulk and surface of the material are provided. The DFT with GGA is used to determine the structure and to calculate the electronic and optical properties of the chemically ordered KTa0.5Nb0.5O3 crystal (100), (110) and (111) surfaces. The results show that the surface properties are different from the bulk properties. The data obtained agree with the expected values and can serve as guidance for future experimental studies in the fields of photorefraction and nonlinear optics.

In this study, we investigated the luminescence properties of erbium-doped potassium tantalite niobate (KTa x Nb1-x O3 or KTN) ceramics, which were prepared by the conventional solid-state reaction synthesis method. In this work, we studied the relationships of the crystal structure, and Raman and photoluminescence (PL) spectra with the tantalum concentration, respectively. The experiments showed that the tantalum dopants modified the intensity of the green, red and near-infrared emission bands. The experiments also showed a blue shift for the 2 mol % erbium doped KTN samples with different tantalum compositions. Doping Ta not only led to the change in PL intensity but also in spectral shapes. The PL spectra showed the splitting peaks for the samples with low Ta compositions. Then these peaks combined and broadened as Ta concentration increase. When Ta was substituted for Nb completely, the luminescence intensity of the green emission band had an increase of approximately about one order of magnitude, which was because of the absence of the first-order phonon relaxation in the high-Ta-concentration samples.