No abstract

Herein, uniform multishelled TiO2 hollow microspheres were synthesized, especially 3- and 4-shelled TiO2 hollow microspheres were synthesized for the first time by a simple sacrificial method capable of controlling the shell thickness, intershell spacing, and number of internal multishells, which are achieved by controlling the size, charge, and diffusion rate of the titanium coordination ions as well as the calcination process. Used as anodes for lithium ion batteries, the multishelled TiO2 hollow microspheres show excellent rate capacity, good cycling performance, and high specific capacity. A superior capacity, up to 237 mAh/g with minimal irreversible capacity after 100 cycles is achieved at a current rate of 1 C (167.5 mA/g), and a capacity of 119 mAh/g is achieved at a current rate of 10 C even after 1200 cycles.

Figure S1. XRD patterns of the CeO 2 hydrothermal treated at 170 o C for (a) 12h, (b) 24h, (c) 48h, (d) 144h.

Strain engineering has emerged as a powerful tool to create new states of known materials with excellent performance. Here, we show a general and practically realizable method via interphase strain to obtain a new super tetragonality providing giant polarization. This method is illustrated for the case of PbTiO3, where we report a c/a ratio of up to 1.238 in epitaxial composite thin films, compared to that of 1.065 in bulk PbTiO3. These thin films of super-tetragonal structure possess an unprecedented giant remanent polarization, 236.3 μC/cm 2 , which is almost twice the value of all known ferroelectrics. The tetragonal phase is stable up to 725 °C as compared to the bulk's transition temperature of 490 °C. The present interphase strain approach could provide a new avenue to enhance the physical properties of materials with respect to their multiferroic, photonic, superconductor, and energy-harvesting behavior.

Most materials expand on heating, known as positive thermal expansion. There are some instances most of which have been discovered in the past decade to exhibit a negative thermal expansion (NTE). [1][2][3][4][5][6][7][8][9] The nature of NTE behavior originates from the effect of atomic vibrations, (e.g., the low-energy transverse mode (ice), 2 the coupled rotation of rigid polyhedra (ZrW 2 O 8 , Fe[Co-(CN) 6 ]), 1,4 and active vibration modes of carbon fullerenes and nanotubes), 7 from the effect of magnetic transition (Invar alloy), 3 or from the changes in electron configuration (Sm 2.72 C 60 , YbCuAl). 8 The occurrence of NTE materials immediately found their important technical applications in many fields, because the overall thermal expansion coefficient (TEC) could be tailored by introduction of NTE materials. 1,2 In particular, zero thermal expansion (ZTE) is very interesting, where the volume neither expands nor contracts with the temperature fluctuation. 3-6 The ZTE could be achieved to form composite by combining the materials with positive thermal expansion with NTE materials. However, the fabrication of ZTE composite is hampered by the poor thermal stability of NTE compounds. For example, ZrW 2 O 8 will be decomposed at a relatively low temperature (777°C). 1 The requirement of ZTE will be satisfied if the ZTE is available in a single phase. Up to now, rare materials exhibit the novel ZTE, such as Invar alloys and Fe-[Co(CN) 6 ]. 3,4 Moreover, the ZTE generally appears in a low temperature (below room temperature). The ZTE over a wider temperature range would be very useful for the applications.PbTiO 3 (PT) as an important perovskite-type multifunctional material exhibits a unique NTE in the perovskite family. 9,10 The unit cell volume of PT contracts over a wide temperature range in the ferroelectric phase (25-490°C) with an average intrinsic volumetric TEC (-1.99 × 10 -5°C-1 ). 9b The NTE of PT-based compounds can be controlled over a large range from -0.11 × 10 -5 to -3.92 × 10 -5°C-1 , which covers the range found in almost all other known NTE oxides. 9 However, a low or ZTE could only be achieved by sacrificing the temperature range, that is, reducing the Curie point (T C ), such as for Pb 0.80 La 0.20 TiO 3 (-0.11 × 10 -5°C -1 , 25-130°C). 9b It is a challenge to expand ZTE to the hightemperature range. On the basis of our previously studied PbTiO 3 -based compounds, we could only access a low expansion or ZTE by reducing the tetragonality (c/a), resulting in the decrease in the ZTE temperature range (region II in Figure 1). To obtain the ZTE in a wider temperature range, a kind of PbTiO 3 -based compound should be found in the region I where c/a is large and the absolute value of TEC is low (Figure 1). Recently, in the PbTiO 3 -BiMeO 3 (Me is cations with an average valence +3), the Bi substitution plays an unusual role in which both T C and c/a are considerably enhanced, owing to the strong coupling between the Pb/Bi cations and the B-site cations with strong ferroelectricity activity, suc...

A general self-templating method is introduced to construct triple-shelled CeO₂ hollow microspheres, which are composed of tiny CeO₂ nanoparticles. When the triple-shelled CeO₂ hollow microspheres are used as photocatalysts for direct water oxidation with AgNO₃ as the electron scavenger, excellent activity and enhanced stability for O₂ evolution are achieved, in contrast with commercial CeO₂ nanoparticles, single-shelled CeO₂ hollow microspheres and double-shelled CeO₂ hollow microspheres. Such an outstanding performance is attributed to the unique properties of the triple-shelled CeO₂ hollow microspheres including more efficient multiple reflections of the incident light by the inner shells, the larger surface area and more active sites for improving separation of electron-hole pairs, and the more curved surfaces unfavorable for deposition of in situ generated Ag nanoparticles.

The rare physical property of zero thermal expansion (ZTE) is intriguing because neither expansion nor contraction occurs with temperature fluctuations. Most ZTE, however, occurs below room temperature. It is a great challenge to achieve isotropic ZTE at high temperatures. Here we report the unconventional isotropic ZTE in the cubic (Sc1-xMx)F3 (M = Ga, Fe) over a wide temperature range (linear coefficient of thermal expansion (CTE), αl = 2.34 × 10(-7) K(-1), 300-900 K). Such a broad temperature range with a considerably negligible CTE has rarely been documented. The present ZTE property has been designed using the introduction of local distortions in the macroscopic cubic lattice by heterogeneous cation substitution for the Sc site. Even though the macroscopic crystallographic structure of (Sc0.85Ga0.05Fe0.1)F3 adheres to the cubic system (Pm3̅m) according to the results of X-ray diffraction, the local structure exhibits a slight rhombohedral distortion. This is confirmed by pair distribution function analysis of synchrotron radiation X-ray total scattering. This local distortion may weaken the contribution from the transverse thermal vibration of fluorine atoms to negative thermal expansion, and thus may presumably be responsible for the ZTE. In addition, the present ZTE compounds of (Sc1-xMx)F3 can be functionalized to exhibit high-Tc ferromagnetism and a narrow-gap semiconductor feature. The present study shows the possibility of obtaining ZTE materials with multifunctionality in future work.

PbTiO(3)-based compounds are well-known ferroelectrics that exhibit a negative thermal expansion more or less in the tetragonal phase. The mechanism of negative thermal expansion has been studied by high-temperature neutron powder diffraction performed on two representative compounds, 0.7PbTiO(3)-0.3BiFeO(3) and 0.7PbTiO(3)-0.3Bi(Zn(1/2)Ti(1/2))O(3), whose negative thermal expansion is contrarily enhanced and weakened, respectively. With increasing temperature up to the Curie temperature, the spontaneous polarization displacement of Pb/Bi (δz(Pb/Bi)) is weakened in 0.7PbTiO(3)-0.3BiFeO(3) but well-maintained in 0.7PbTiO(3)-0.3Bi(Zn(1/2)Ti(1/2))O(3). There is an apparent correlation between tetragonality (c/a) and spontaneous polarization. Direct experimental evidence indicates that the spontaneous polarization originating from Pb/Bi-O hybridization is strongly associated with the negative thermal expansion. This mechanism can be used as a guide for the future design of negative thermal expansion of phase-transforming oxides.