The search for active semiconductor photocatalysts that directly split water under visible-light irradiation remains one of the most challenging tasks for solar-energy utilization. Over the past 30 years, the search for such materials has focused mainly on metal-ion substitution as in In(1-x)Ni(x)TaO(4) and (V-,Fe- or Mn-)TiO(2) (refs 7,8), non-metal-ion substitution as in TiO(2-x)N(x) and Sm(2)Ti(2)O(5)S(2) (refs 9,10) or solid-solution fabrication as in (Ga(1-x)Zn(x))(N(1-x)O(x)) and ZnS-CuInS(2)-AgInS(2) (refs 11,12). Here we report a new use of Ag(3)PO(4) semiconductor, which can harness visible light to oxidize water as well as decompose organic contaminants in aqueous solution. This suggests its potential as a photofunctional material for both water splitting and waste-water cleaning. More generally, it suggests the incorporation of p block elements and alkali or alkaline earth ions into a simple oxide of narrow bandgap as a strategy to design new photoelectrodes or photocatalysts.

The immense potential of colossal permittivity (CP) materials for use in modern microelectronics as well as for high-energy-density storage applications has propelled much recent research and development. Despite the discovery of several new classes of CP materials, the development of such materials with the required high performance is still a highly challenging task. Here, we propose a new electron-pinned, defect-dipole route to ideal CP behaviour, where hopping electrons are localized by designated lattice defect states to generate giant defect-dipoles and result in high-performance CP materials. We present a concrete example, (Nb+In) co-doped TiO₂ rutile, that exhibits a largely temperature- and frequency-independent colossal permittivity (> 10(4)) as well as a low dielectric loss (mostly < 0.05) over a very broad temperature range from 80 to 450 K. A systematic defect analysis coupled with density functional theory modelling suggests that 'triangular' In₂(3+)Vo(••)Ti(3+) and 'diamond' shaped Nb₂(5+)Ti(3+)A(Ti) (A = Ti(3+)/In(3+)/Ti(4+)) defect complexes are strongly correlated, giving rise to large defect-dipole clusters containing highly localized electrons that are together responsible for the excellent CP properties observed in co-doped TiO₂. This combined experimental and theoretical work opens up a promising feasible route to the systematic development of new high-performance CP materials via defect engineering.

Energy storage materials and their applications have long been areas of intense research interest for both the academic and industry communities. Dielectric capacitors using antiferroelectric materials are capable of displaying higher energy densities as well as higher power/charge release densities by comparison with their ferroelectric and linear dielectric counterparts and therefore have greater potential for practical energy storage applications. Over the past decade, extensive efforts have This article is protected by copyright. All rights reserved. 2been devoted to the development of high performance, antiferroelectric, energy storage ceramics and much progress has been achieved. In this review, the current state-of-the-art as regards antiferroelectric ceramic systems, including PbZrO 3 -based, AgNbO 3 -based and (Bi,Na)TiO 3 -based systems, are comprehensively summarized with regards to their energy storage performance. Strategies are then discussed for the further improvement of the energy storage properties of these antiferroelectric ceramic systems. This is followed by a review of the low temperature sintering techniques and the charge-discharge performance of antiferroelectric ceramics from a practical point of view. The review will be of benefit for researchers in the area as it offers a quick overview of recent progress in the development of various kinds of antiferroelectric ceramics and their properties. It should also stimulate the development of novel antiferroelectric ceramics with high energy storage performance.

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The displacive ferroelectric