Crystal structure and oxygen stoichiometry in <mml:math display="inline"><mml:mrow><mml:msub><mml:mi>LiMn</mml:mi><mml:mrow><mml:mn>1.5</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi>Ni</mml:mi><mml:mrow><mml:mn>0.5</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>4</mml:mn><mml:mo>−</mml:mo><mml:mi>δ</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>LiMn1.5Ni0.5O4−δ , a potential lithium-battery cathode, vary with temperature, as observed in samples quenched from different temperatures and by in situ diffraction and thermogravimetry techniques. When prepared in high <mml:math display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>O2 pressure, this cation-ordered spinel is oxygen-stoichiometric, <mml:math display="inline"><mml:mrow><mml:mi>δ</mml:mi><mml:mo>=</mml:mo><mml:mn>0</mml:mn></mml:mrow></mml:math>δ=0 , space group <mml:math display="inline"><mml:mrow><mml:mi>P</mml:mi><mml:msub><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub><mml:mn>32</mml:mn></mml:mrow></mml:math>P4332 . Upon heating between 650 and <mml:math display="inline"><mml:mrow><mml:mn>680</mml:mn><mml:mo>°</mml:mo><mml:mi mathvariant="normal">C</mml:mi></mml:mrow></mml:math>680°C , increasing oxygen deficiency occurs exclusively in <mml:math display="inline"><mml:mrow><mml:msub><mml:mi>MnO</mml:mi><mml:mrow><mml:mn>6</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>MnO6 octahedra and <mml:math display="inline"><mml:mrow><mml:mi>Mn</mml:mi><mml:mo>–</mml:mo><mml:mi mathvariant="normal">O</mml:mi><mml:mo>–</mml:mo><mml:mi>Mn</mml:mi></mml:mrow></mml:math>Mn–O–Mn bonds, which induces a volume increase of the 12d octahedra, a reduction of Mn as shown by X-ray absorption near-edge structure, equalization of <mml:math display="inline"><mml:mrow><mml:mi>Mn</mml:mi><mml:mo>–</mml:mo><mml:mi mathvariant="normal">O</mml:mi></mml:mrow></mml:math>Mn–O and <mml:math display="inline"><mml:mrow><mml:mi>Ni</mml:mi><mml:mo>–</mml:mo><mml:mi mathvariant="normal">O</mml:mi></mml:mrow></mml:math>Ni–O bond lengths, and disordering of Mn, Ni on octahedral sites. Hence, the transformation to space group <mml:math display="inline"><mml:mrow><mml:mi>F</mml:mi><mml:mi>d</mml:mi><mml:mover accent="true"><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mo stretchy="false">¯</mml:mo></mml:mover><mml:mi>m</mml:mi></mml:mrow></mml:math>Fd3¯m , shown by Rietveld refinement of variable-temperature neutron diffraction data, is a direct consequence of oxygen loss from the structure. On further oxygen loss, a second phase transformation occurs to give a cation-deficient cubic rock salt phase, <mml:math display="inline"><mml:mrow><mml:mi>δ</mml:mi><mml:mo>∼</mml:mo><mml:mn>0.65</mml:mn></mml:mrow></mml:math>δ∼0.65 , at <mml:math display="inline"><mml:mrow><mml:mn>950</mml:mn><mml:mo>°</mml:mo><mml:mi mathvariant="normal">C</mml:mi></mml:mrow></mml:math>950°C , which loses more oxygen at higher temperatures until, at <mml:math display="inline"><mml:mrow><mml:mn>1100</mml:mn><mml:mo>°</mml:mo><mml:mi mathvariant="normal">C</mml:mi></mml:mrow></mml:math>1100°C , the material is essentially a stoichiometric, single-phase cation-disordered rock salt, space group <mml:math display="inline"><mml:mrow><mml:mi>F</mml:mi><mml:mi>m</mml:mi><mml:mover accent="true"><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mo stretchy="false">¯</mml:mo></mml:mover><mml:mi>m</mml:mi></mml:mrow></mml:math>Fm3¯m . A second spinel phase persists in small amounts from 950 to <mml:math display="inline"><mml:mrow><mml:mn>1100</mml:mn><mml:mo>°</mml:mo><mml:mi mathvariant="normal">C</mml:mi></mml:mrow></mml:math>1100°C . Differences in electrochemical behavior depend on sample preparation and correlate with the oxygen content of <mml:math display="inline"><mml:mrow><mml:msub><mml:mi>LiMn</mml:mi><mml:mrow><mml:mn>1.5</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi>Ni</mml:mi><mml:mrow><mml:mn>0.5</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>4</mml:mn><mml:mo>−</mml:mo><mml:mi>δ</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>LiMn1.5Ni0.5O4−δ when used as a cathode in Li test cells.

Disinfection residuals in drinking water protect water quality and public heath by limiting planktonic microbial regrowth during distribution. However, we do not consider the consequences and selective pressures of such residuals on the ubiquitous biofilms that persist on the vast internal surface area of drinking water distribution systems. Using a full scale experimental facility, integrated analyses were applied to determine the physical, chemical and biological impacts of different free chlorine regimes on biofilm characteristics (composition, structure and microbiome) and water quality. Unexpectedly, higher free chlorine concentrations resulted in greater water quality degredation, observable as elevated inorganic loading and greater discolouration (a major cause of water quality complaints and a mask for other failures). High-chlorine concentrations also reduced biofilm cell concentrations but selected for a distinct biofilm bacterial community and inorganic composition, presenting unique risks. The results challenge the assumption that a measurable free chlorine residual necessarily assures drinking water safety.