A structure, conductivity and dielectric properties investigation of A3CoNb2O9 (A=Ca2+, Sr2+, Ba2+) triple perovskites

Relaxor ferroelectric-like glassy dielectric dispersion in the triple perovskite Ba3CoSb2O9

In this work, the dielectric response of polycrystalline Ba3CoSb2O9 was studied as a function of temperature (30 to 900 °C) and frequency (10 Hz to 10 MHz). The triple perovskite Ba3CoSb2O9 was successfully synthesized and characterized for structural and dielectric properties. The Rietveld analysis of the X-ray diffractogram confirms the formation of a hexagonal phase with P63/mmc symmetry. This centrosymmetric 3(BaCo1/3Sb2/3O3) perovskite shows structural similarity to a prototypical non-centrosymmetric relaxor ferroelectric, PbMg1/3Nb2/3O3. The dielectric constant, ε', follows a non-Debye Cole-Cole relation and exhibits anomalous responses such as: (a) a thermally activated colossal dielectric constant (>105) and (b) a highly dispersive peak maximum (523-853 K). The real part of ac conductivity, σ', also shows a change of approximately 6 orders in magnitude (10-8 to 10-2 S m-1). Validation of Jonscher's law and impedance (Nyquist plot) and modulus (M'') analyses indicate that hopping polarization is the predominant thermally activated mechanism. Moreover, the large value of ε' and its dispersion were found to be highly correlated with the underlying crystal structure and were attributed to the local ionic site ordering. The study suggests that the anomalous dielectric dispersion must have an intrinsic origin.

Mn3MnNb2O9: high-pressure triple perovskite with 1 : 2 B-site order and modulated spins

The first triple perovskite with Mn in A- and 1 : 2 B-site order Mn₃MnNb₂O₉, prepared using high pressure phase transformation of the magnetodielectric Mn₄Nb₂O₉, is reported herein. It has a complex magnetic behaviour with a transition from a collinear AFM into an evolving incommensurate spin density wave (SDW) further stabilised into a lock-in structure dictated by the B-site order.

Efficient Solar Energy Conversion Using CaCu3Ti4O12 Photoanode for Photocatalysis and Photoelectrocatalysis

A highly efficient third generation catalyst, CaCu₃Ti₄O₁₂ (CCTO) shows excellent photoelectrochemical (PEC) and photocatalytic ability. As only 4% part of the solar spectrum covers UV light, thus it is highly desirable to develop visible light active photocatalyst materials like CCTO for effective solar energy conversion. A direct band transition with a narrow band gap (1.5 eV) was observed. Under light irradiation, high photocurrent density was found to be 0.96 mA/cm², indicating the visible light induced photocatalytic ability of CCTO. Visible light mediated photocatalytic and photoelectrocatalytic degradation efficiency of CaCu₃Ti₄O₁₂ pellets (CCTO) was investigated for three classes of pharmaceutical waste: erythrosin (dye), ciprofloxacin (antibiotic) and estriol (steroid). It is found that the degradation process follows first order kinetic reaction in electrocatalysis, photocatalysis and photoelectrocatalysis and high kinetic rate constant was observed in photoelectrocatalysis. This was quite high in comparison to previously reported methods.

Polyaniline/CaCu3Ti4O12 nanofiber composite with a synergistic effect on visible light photocatalysis

CaCu₃Ti₄O₁₂ (CCTO)–polyaniline (PANI) nanofiber composites with different ratios of PANI/CCTO were successfully prepared by in situ polymerization and were shown to be active photocatalysts under irradiation with visible light.

Reported and predicted structures of Ba(Co,Nb)1−δO3 hexagonal perovskite phases

The Extended Module Materials Assembly method was implemented for close-packed hexagonal structures and applied to doped barium niobate perovskites.