Composition, crystal structures, polymorphic transformations, and stability of the thermoelectric material known in the literature as "Zn 4 Sb 3 " have been studied on a polycrystalline sample and Bi-flux-grown single crystals using X-ray diffraction techniques, resistance, and Seebeck coefficient measurements at various temperatures ranging from 4 to 773 K. Microprobe analysis yields the composition of the flux-grown crystals to be close to Zn 13 Sb 10 , with minor Bi doping. High-temperature X-ray and Seebeck coefficient studies show that the phase is unstable at high temperatures in a vacuum because of Zn losses. Both X-ray diffraction and resistivity measurements indicate the presence of two consecutive symmetry-breaking transitions below room temperature, in agreement with our previous results on polycrystalline samples. Application of Landau theory suggests that the first R3c → C2/c symmetry breaking may be second-order in nature. The second, lowtemperature symmetry breaking may proceed along two routes. One of these pathways, a first-order C2/c → C1 symmetry reduction, may lead to an incommensurate structure and is consistent with our experimental observations. Disciplines

The effects of laser wavelength (355 nm and 532 nm) and laser pulse energy on the quantitative analysis of LiFePO₄ by atom probe tomography are considered. A systematic investigation of ultraviolet (UV, 355 nm) and green (532 nm) laser assisted field evaporation has revealed distinctly different behaviors. With the use of a UV laser, the major issue was identified as the preferential loss of oxygen (up to 10 at%) while other elements (Li, Fe and P) were observed to be close to nominal ratios. Lowering the laser energy per pulse to 1 pJ/pulse from 50 pJ/pulse increased the observed oxygen concentration to nearer its correct stoichiometry, which was also well correlated with systematically higher concentrations of (16)O₂(+) ions. Green laser assisted field evaporation led to the selective loss of Li (~33% deficiency) and a relatively minor O deficiency. The loss of Li is likely a result of selective dc evaporation of Li between or after laser pulses. Comparison of the UV and green laser data suggests that the green wavelength energy was absorbed less efficiently than the UV wavelength because of differences in absorption at 355 and 532 nm for LiFePO₄. Plotting of multihit events on Saxey plots also revealed a strong neutral O2 loss from molecular dissociation, but quantification of this loss was insufficient to account for the observed oxygen deficiency.

Lithium iron borate (LiFeBO 3 ) is a particularly desirable cathode material for lithium-ion batteries due to its high theoretical capacity (220 mA h g À1 ) and its favorable chemical constituents, which are abundant, inexpensive and non-toxic. However, its electrochemical performance appears to be severely hindered by the degradation that results from air or moisture exposure. The degradation of LiFeBO 3 was studied through a wide array of ex situ and in situ techniques (X-ray diffraction, nuclear magnetic resonance, X-ray absorption spectroscopy, electron microscopy and spectroscopy) to better understand the possible degradation process and to develop methods for preventing degradation. It is demonstrated that degradation involves both Li loss from the framework of LiFeBO 3 and partial oxidation of Fe(II), resulting in the creation of a stable lithium-deficient phase with a similar crystal structure to LiFeBO 3 . Considerable LiFeBO 3 degradation occurs during electrode fabrication, which greatly reduces the accessible capacity of LiFeBO 3 under all but the most stringently controlled conditions for electrode fabrication. Comparative studies on micron-sized LiFeBO 3 and nanoscale LiFeBO 3 -carbon composite showed a very limited penetration depth ($30 nm) of the degradation phase front into the LiFeBO 3 core under near-ambient conditions. Two-phase reaction regions during delithiation and lithiation of LiFeBO 3 were unambiguously identified through the galvanostatic intermittent titration technique (GITT), although it is still an open question as to whether the twophase reaction persists across the whole range of possible Li contents. In addition to the main intercalation process with a thermodynamic potential of 2.8 V, there appears to be a second reversible electrochemical process with a potential of 1.8 V. The best electrochemical performance of LiFeBO 3 was ultimately achieved by introducing carbon to minimize the crystallite size and strictly limiting air and moisture exposure to inhibit degradation.