The rechargeable lithium-ion cell is an advanced energy-storage system. However, high cost, safety hazards, and chemical instability prohibit its use in large-scale applications. An alternative cathode material, LiFePO(4), solves these problems, but has a kinetic problem involving strong electron/hole localization. One reason for this is believed to be the limited carrier density in the fixed monovalent Fe(3+)PO(4)/LiFe(2+)PO(4) two-phase electrode reaction in LixFePO4. Here, we provide experimental evidence that LixFePO4, at room temperature, can be described as a mixture of the Fe(3+)/Fe(2+) mixed-valent intermediate LialphaFePO4 and Li1-betaFePO4 phases. Using powder neutron diffraction, the site occupancy numbers for lithium in each phase were refined to be alpha=0.05 and 1-beta=0.89. The corresponding solid solution ranges outside the miscibility gap (0

No abstract

A series of synthetic heterosite-purpurite, (Mn y Fe 1-y )PO 4 (y < 0.8), with negligible disorder and impurities, was obtained by chemical oxidation of the well-crystallized isotypic tryphillite-lithiophilite series, Li(Mn y Fe 1-y )PO 4 (ordered olivine structure, space group Pnma). Comparative magnetic and X-ray/ neutron powder diffraction investigations of the two solid-solution lines were performed as a function of Mn content to increase understanding of the electrochemical activity loss of Mn 3+ /Mn 2+ in the Li x (Mn y Fe 1-y )PO 4 electrode system. Introducing Mn ions into the 4c site did not cause significant change in the local geometry of M 2+ O 6 and PO 4 polyhedra, while the M 3+ O 6 octahedra became severely distorted with an increase in the number of Jahn-Teller active Mn 3+ ions. The edge-sharing geometry of M 3+ O 6 and PO 4 polyhedra fixed the shared O3′-O3′ interatomic distance, causing selective strong elongation of the M 3+ -O3′ distance with small shrinkage of other M 3+ -O1, M 3+ -O2, and M 3+ -O3 bond lengths. The overall distortion of the MO 6 octahedra with M ) Mn 3+ was much larger than the corresponding change in the unit-cell orthorombicity and significantly increased asymmetry in the M-O-M superexchange interaction. All samples exhibited antiferromagnetism; however, the trivalent series had more than a sevenfold larger decrease in Neel temperature T N (from ca. 130 K at y ) 0 to ca. 50 K at y ) 0.8) compared to the divalent series (from ca. 52 K at y ) 0 to ca. 35 K at y )1) as a function of the Mn content y.

No abstract

A trenching method was used to determine the contribution of root respiration to soil respiration. Soil respiration rates in a trenched plot (Rtrench) and in a control plot (Rcontroi) were measured from May 2000 to September 2001by using an open-flow gas exchange system with an infrared gas analyser. The decomposition rate of dead roots (Ro) was estimated by using a root-bag method to correct the soil respiration measured from the trenched plots for the additional decaying root biomass. The soil respiration rates in the control plot increased from May (240-320 mg C02 m-2 h-1 ) to August (840-1150 mg C02 m-2 h-i ) and then decreased during autumn (200-650 mg C02 m-2 h-1 ). The soil respiration rates in the trenched plot showed a similar pattern of seasonal change, but the rates were lower than in the control plot except during the 2 months following the trenching. Root respiration rate (Rr) and heterotrophic respiration rate (Rh) were estimated from Rcontrol, Rtrench, and Ro. We estimated that the contribution of Rr to total soil respiration in the growing season ranged from 27 to 71 %. There was a significant relationship between Rh and soil temperature, whereas Rr had no significant correlation with soil temperature. The results suggest that the factors controlling the seasonal change of respiration differ between the two components of soil respiration, Rr and Rh.Abbreviations: Ro -carbon emission due to the decomposition of residual roots; Rh -heterotrophic respiration rate; Rr -root respiration rate; NEP -net ecosystem production; NPP -net primary productivity

The effects of rainfall events on soil CO2 fluxes were examined in a cool temperate Quercus/Betula forest in Japan. The soil CO2 fluxes were measured using an open‐flow gas exchange system with an infrared gas analyzer in the snow‐free season from August 1999 to November 2000. Soil CO2 flux showed no significant diurnal trend on days without rain. In contrast, rainfall events caused a significant increase in soil CO2 flux. To determine the effect of rainfall events and to evaluate more precisely the daily and annual soil carbon flux, we constructed a multiple polynomial regression model that included two variables, soil temperature and soil water content, using the soil CO2 flux data recorded on sunny days. Daily soil carbon fluxes on sunny days calculated by the model were almost the same as those determined by the field measurements. On the contrary, the fluxes measured on rainy days were significantly higher than those calculated daily from the soil carbon fluxes by the model. Annual soil carbon fluxes in 1999 and 2000 were estimated using models that both do and do not take rainfall effects into consideration. The result indicates that post‐rainfall increases in soil CO2 flux represent approximately 16–21% of the annual soil carbon flux in this cool temperate deciduous forest.

No abstract

Diurnal changes in photosynthetic gas exchange and chlorophyll fluorescence were measured under full sunlight to reveal diffusional and non‐diffusional limitations to diurnal assimilation in leaves of Arisaema heterophyllum Blume plants grown either in a riparian forest understorey (shade leaves) or in an adjacent deforested open site (sun leaves). Midday depressions of assimilation rate (A) and leaf conductance of water vapour were remarkably deeper in shade leaves than in sun leaves. To evaluate the diffusional (i.e. stomatal and leaf internal) limitation to assimilation, we used an index [1–A/A350], in which A350 is A at a chloroplast CO2 concentration of 350 μmol mol−1. A350 was estimated from the electron transport rate (JT), determined fluorometrically, and the specificity factor of Rubisco (S), determined by gas exchange techniques. In sun leaves under saturating light, the index obtained after the ‘peak’ of diurnal assimilation was 70% greater than that obtained before the ‘peak’, but in shade leaves, it was only 20% greater. The photochemical efficiency of photosystem II (ΔF/Fm′) and thus JT was considerably lower in shade leaves than in sun leaves, especially after the ‘peak’. In shade leaves but not in sun leaves, A at a photosynthetically active photon flux density (PPFD) > 500 μmol m−2 s−1 depended positively on JT throughout the day. Electron flows used by the carboxylation and oxygenation (JO) of RuBP were estimated from A and JT. In sun leaves, the JO/JT ratio was significantly higher after the ‘peak’, but little difference was found in shade leaves. Photorespiratory CO2 efflux in the absence of atmospheric CO2 was about three times higher in sun leaves than in shade leaves. We attribute the midday depression of assimilation in sun leaves to the increased rate of photorespiration caused by stomatal closure, and that in shade leaves to severe photoinhibition. Thus, for sun leaves, increased capacities for photorespiration and non‐photochemical quenching are essential to avoid photoinhibitory damage and to tolerate high leaf temperatures and water stress under excess light. The increased Rubisco content in sun leaves, which has been recognized as raising photosynthetic assimilation capacity, also contributes to increase in the capacity for photorespiration.