ZnTaO₂N: Stabilized High-Temperature LiNbO₃-type Structure

Abstract

By using a high-pressure reaction, we prepared a new oxynitride ZnTaON that crystallizes in a centrosymmetric (R3̅c) high-temperature LiNbO-type structure (HTLN-type). The stabilization of the HTLN-type structure down to low temperatures (at least 20 K) makes it possible to investigate not only the stability of this phase, but also the phase transition to a noncentrosymmetric (R3c) LiNbO-type structure (LN-type) which is yet to be clarified. Synchrotron and neutron diffraction studies in combination with transmission electron microscopy show that Zn is located at a disordered 12c site instead of 6a, implying an order-disorder mechanism of the phase transition. It is found that the closed d-shell of Zn, as well as the high-valent Ta ion, is responsible for the stabilization of the HTLN-type structure, affording a novel quasitriangular ZnON coordination. Interestingly, only 3% Zn substitution for MnTaON induces a phase transition from LN- to HTLN-type structure, implying the proximity in energy between the two structural types, which is supported by the first-principles calculations.

Zinc Tantalum Oxynitride (ZnTaO2N) Photoanode Modified with Cobalt Phosphate Layers for the Photoelectrochemical Oxidation of Alkali Water

“…Figure 1 demonstrates the XRD patterns for the TaON, ZnTaO 2 N, and CoPi/ZnTaO 2 N photoanodes that were fabricated by EPD followed by loading CoPi using photodeposition methods on ITO substrates, and annealing in a nitrogen atmosphere at 450 °C. The XRD pattern of as-synthesized ZnTaO 2 N reveals that all the major peaks can be assigned to a perovskite-type phase that is structurally similar to that of ZnTaO 2 N [ 28 ]. The TaON XRD pattern obtained was consistent with the formation of the baddeleyite (monoclinic ZrO 2 ) structure.…”

“…Domen et al demonstrated TaON/co-catalyst-based photoanodes with an incident photon-to-electron conversion efficiency (IPCE) of 76% at 400 nm for water oxidation at a minimal or no external applied bias [ 20 , 21 , 22 , 23 , 24 , 25 , 26 ]. Since then, oxynitrides, such as LaTiO 2 N [ 22 ], SrNbO 2 N [ 27 , 28 ], BaNbO 2 N [ 29 ], among other materials, have been similarly developed as photoanodes [ 30 , 31 , 32 , 33 , 34 , 35 ]. Few of these have attained superior IPCEs of the order of magnitude of several tens of percent with an externally applied bias that is less than the thermodynamically mandatory oxidation potential (1.23 V) for water electrolysis.…”

“…Several such photoanodes have been developed, e.g., BaNbO 2 N [ 21 ], CoO x /LaTiO 2 N [ 22 ], and BaZrO 3 /BaTaO 2 N [ 33 ], which have been found to utilize the absorption of visible-light in addition to appropriate sacrificial reagents. SrNbO 2 N-based photoanodes (BG < 2 eV), function as water-oxidation catalysts with the support of a co-catalyst in visible-light illuminations [ 27 , 28 , 34 ]. However, the recombination of the photoexcited carriers and poor photon absorption efficiencies are considered as major drawbacks with these systems, and these attributes need to be improved for application in water-splitting reactions.…”

Density Functional Perturbation Theory to Predict Piezoelectric Properties

“…For example, LiNbO 3 - Density Functional Perturbation Theory to Predict Piezoelectric Properties http://dx.doi.org/10.5772/intechopen.76827 type structured ZnSbO 3 was successfully synthesized [39] under high pressure, and improvement of the spontaneous polarization is suggested by enhancement of the covalency of Sn site from first-principles simulation [40]. Moreover, high-pressure synthesized research on LiNbO 3type structure is now extended to more complex compounds such as oxynitrides [41,42].…”

Theoretical and Experimental Investigations into Novel Oxynitride Discovery in the GaN-TiO2 System at High Pressure

“…Since oxygen and nitrogen have similar ionic size, electronegativities and coordination number, these anions are usually disordered across anion sites [9], and hence makes it a real challenge for crystal structure prediction methods. Partial ordering have been observed in some oxynitrides [24][25][26], however, ideally ordered oxynitrides are scarce between known oxynitrides e.g., TaON and Si 2 N 2 O [27,28]. While incorporating disorder is not practical with crystal structure prediction methods at the current stage of development, the predicted structures give insights into the chemistry of the system, may guide experimental efforts, and contain structural features, such as the separation of Ti and Ga into different structural blocks, which is confirmed in the experimental analysis.…”