Structural Phase Transition from Rhombohedral (<i>R</i>3̅<i>m</i>) to Monoclinic (<i>C</i>2/<i>m</i>) Symmetry in Lithium Overstoichiometric Li_1+δCo_1−δO_2−δ

Stoichiometric lithium cobalt oxide LiCoO₂ is known to exhibit several structural phase transitions with <i>x</i> in Li_<i>x</i>CoO₂ at ambient temperature (<i>T</i>); e.g., an initial rhombohedral (<i>R</i>3̅<i>m</i>) phase transforms into a monoclinic (<i>C</i>2/<i>m</i>) phase at <i>x</i> ∼ 0.5. In contrast, lithium overstoichiometric (Li)_3<i>b</i>[Li_δCo_1−δ]_3<i>a</i>O_2−δ with δ ≥ ∼0.02, where δ is the Li⁺ ions at the 3<i>a</i> (Co) site, maintains the <i>R</i>3̅<i>m</i> symmetry until <i>x</i> ∼ 0.5 in Li_<i>x</i>(Li_δCo_1−δ)­O_2−δ at ambient <i>T</i>, and this is the reason why such material has been widely used in commercial lithium ion batteries. We performed X-ray diffraction measurements in the <i>T</i> range between 100 and 300 K for the lithium overstoichiometric Li_<i>x</i>(Li_0.02Co_0.98)­O_1.98 samples with <i>x</i> = 1, 0.56, and 0.51 to understand the factors that govern the structural changes in Li_<i>x</i>(Li_δCo_1−δ)­O_2−δ with δ ≥ 0. Both <i>x</i> = 0.56 and 0.51 samples exhibit a structural phase transition from the high-<i>T R</i>3̅<i>m</i> phase to the low-<i>T C</i>2/<i>m</i> phase at 250 K (=<i>T</i>_s1). Furthermore, these samples indicate another structural phase transition at 170 K (=<i>T</i>_s2); although their crystal structures still have the <i>C</i>2/<i>m</i> symmetry, the degree of monoclinic distortion starts to decrease below <i>T</i>_s2, associated with a magnetic anomaly and a freezing of the Li⁺ ions at the 3<i>b</i> site. Because the two structural phase transitions of <i>T</i>_s1 (=330 K) and <i>T</i>_s2 (=150 K) are also observed for the stoichiometric Li_<i>x</i>CoO₂ compound with <i>x</i> ∼ 0.5, the <i>C</i>2/<i>m</i> phase in Li_<i>x</i>(Li_δCo_1−δ)­O_2−δ is found to appear in the limited <i>x</i> and <i>T</i> ranges. The characteristics and possible origin of <i>T</i>_s1 and <i>T</i>_s2 for both stoichiometric Li_<i>x</i>CoO₂ and lithium overstoichiometric Li_<i>x</i>(Li_0.02Co_0.98)­O_1.98 samples are discussed

Factors associated with colonic diverticulosis on multivariate analysis.

<p>^* The smoking index was evaluated among ever and daily smokers and was defined as the number of cigarettes per day multiplied by the number of smoking years.</p

Prevalence of diverticulosis and anatomic distribution by alcohol consumption (A) and smoking index (B) (n = 2,164).

<p>Right-sided and bilateral diverticula increased significantly in line with amount of alcohol consumption (A). All distribution types of colonic diverticula increased significantly in line with smoking index (SI) (B).</p

Prevalence of diverticulosis (A) and anatomic distribution (B) by age category (n = 2,164).

<p>Colonic diverticulosis increased with age (A). The prevalence of right-sided diverticula was high at for younger age, while left-sided and bilateral types increased with age (B).</p