(Ca0.5Mn0.5)2MnTeO6 - An Anomalously Stable High-Pressure Double Perovskite.

High pressure high temperature treatments of the composition CaMnMnTeO6 are found to yield only an A2BB'O6-type double perovskite (Ca0.5Mn0.5)2MnTeO6, rather than a AA'BB'O6 double double perovskite with A- and B- site cation order as found in analogs CaMnMnReO6 and CaMnMnWO6 with similar cation sizes. Double perovskite (Ca0.5Mn0.5)2MnTeO6 adopts a monoclinic structure in space group P21/n with a framework of highly tilted MnO6 and TeO6 octahedra enclosing disordered Ca2+ and Mn2+ cations. Magnetic measurements show that (Ca0.5Mn0.5)2MnTeO6 is a highly frustrated spin glass with a freezing transition at 5 K, and no long-range spin order is apparent by neutron diffraction at 1.6 K.

Ultrasmall superparamagnetic iron oxide nanoparticles for enhanced tumor penetration.

The intrinsic pathological characteristics of tumor microenvironments restrict the deep penetration of nanomedicines by passive diffusion. Magnetophoresis is a promising strategy to improve the tumor penetration of nanomedicines aided by the external magnetic propulsive force. However, the research thus far has been focused on large nanoparticles, while ultrasmall superparamagnetic iron oxide (Fe3O4) nanoparticles (<∼20 nm) exhibit better performance in many applications such as cancer diagnosis and treatment. Herein, we aim to determine and understand the penetration of ultrasmall Fe3O4 nanoparticles with various sizes, shapes, surface charges and magnetizations in a 3D tumor spheroid model. The behaviour of the nanoparticles of three sizes (10, 15 and 21 nm), two shapes (spherical and octahedral), and opposite surface charges (negative and positive) was investigated. The results demonstrate that magnetically directed penetration works effectively on ultrasmall Fe3O4 nanoparticles. In the absence of a magnetic field, the shape and the surface charge of the ultrasmall magnetic nanoparticles have a more pronounced effect on their penetration compared to their dimensions. While in the presence of a magnetic field, the advantage of larger magnetic nanoparticles was obvious because they experience higher magnetic driving force due to their higher magnetic moments. Overall, relatively large (21 nm), spherical, and positively charged ultrasmall Fe3O4 nanoparticles showed greater penetration in tumors under a magnetic field. Furthermore, our findings suggest that the penetration efficiency of Fe3O4 nanoparticles is closely related to their cellular internalization ability. Therefore, optimization of the cellular uptake and of the magnetization of magnetic nanoparticles should be considered simultaneously for maximizing their penetration in tumor tissue through magnetophoresis.

A New Cation-Ordered Structure Type with Multiple Thermal Redistributions in Co2 InSbO6.

Cation ordering in solids is important for controlling physical properties and leads to ilmenite (FeTiO3 ) and LiNbO3 type derivatives of the corundum structure, with ferroelectricity resulting from breaking of inversion symmetry in the latter. However, a hypothetical third ABO3 derivative with R32 symmetry has never been observed. Here we show that Co2 InSbO6 recovered from high pressure has a new, ordered-R32 A2 BCO6 variant of the corundum structure. Co2 InSbO6 is also remarkable for showing two cation redistributions, to (Co0.5 In0.5 )2 CoSbO6 and then Co2 InSbO6 variants of the ordered-LiNbO3 A2 BCO6 structure on heating. The cation distributions change magnetic properties as the final ordered-LiNbO3 product has a sharp ferrimagnetic transition unlike the initial ordered-R32 phase. Future syntheses of metastable corundum derivatives at pressure are likely to reveal other cation-redistribution pathways, and may enable ABO3 materials with the R32 structure to be discovered.

Double Double to Double Perovskite Transformations in Quaternary Manganese Oxides.

Control of cation ordering in ABX3 perovskites is important to structural, physical and chemical properties. Here we show that thermal transformations of AA'BB'O6 double double perovskites, where both A and B sites have 1:1 cation order, to (A0.5 A'0.5 )2 BB'O6 double perovskites with fully disordered A/A' cations can be achieved under pressure in CaMnMnWO6 and SmMnMnTaO6 , enabling both polymorphs of each material to be recovered. This leads to a dramatic switch of magnetic properties from ferrimagnetic order in double double perovskite CaMnMnWO6 to spin glass behaviour in the highly frustrated double perovskite polymorph. Comparison of double double and double perovskite polymorphs of other materials will enable effects of cation order and disorder on other properties such as ferroelectricity and conductivity to be explored.

Lock-in spin structures and ferrimagnetism in polar Ni2-xCoxScSbO6 oxides.

The new phase Co2ScSbO6 and Ni2-xCoxScSbO6 solid solutions adopt the polar Ni3TeO6-type structure and order magnetically below 60 K. A series of long-period lock-in [0 0 1/3n] spin structures with n = 5, 6, 8 and 10 is discovered, coexisting with a ferrimagnetic [0 0 0] phase at high Co-contents. The presence of electrical polarisation and spontaneous magnetisations offers possibilities for multiferroic properties.