4 research outputs found
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<sub>1+δ</sub>Co<sub>1−δ</sub>O<sub>2−δ</sub>
Stoichiometric lithium cobalt oxide
LiCoO<sub>2</sub> is known
to exhibit several structural phase transitions with <i>x</i> in Li<sub><i>x</i></sub>CoO<sub>2</sub> 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)<sub>3<i>b</i></sub>[Li<sub>δ</sub>Co<sub>1−δ</sub>]<sub>3<i>a</i></sub>O<sub>2−δ</sub> with δ ≥
∼0.02, where δ is the Li<sup>+</sup> ions at the 3<i>a</i> (Co) site, maintains the <i>R</i>3Ì…<i>m</i> symmetry until <i>x</i> ∼ 0.5 in Li<sub><i>x</i></sub>(Li<sub>δ</sub>Co<sub>1−δ</sub>)ÂO<sub>2−δ</sub> 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<sub><i>x</i></sub>(Li<sub>0.02</sub>Co<sub>0.98</sub>)ÂO<sub>1.98</sub> samples with <i>x</i> = 1, 0.56, and 0.51 to understand the factors that govern the structural
changes in Li<sub><i>x</i></sub>(Li<sub>δ</sub>Co<sub>1−δ</sub>)ÂO<sub>2−δ</sub> 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>3Ì…<i>m</i> phase to the low-<i>T C</i>2/<i>m</i> phase at 250 K (=<i>T</i><sub>s1</sub>). Furthermore,
these samples indicate another structural phase transition at 170
K (=<i>T</i><sub>s2</sub>); 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><sub>s2</sub>, associated with a magnetic anomaly and a freezing
of the Li<sup>+</sup> ions at the 3<i>b</i> site. Because
the two structural phase transitions of <i>T</i><sub>s1</sub> (=330 K) and <i>T</i><sub>s2</sub> (=150 K) are also observed
for the stoichiometric Li<sub><i>x</i></sub>CoO<sub>2</sub> compound with <i>x</i> ∼ 0.5, the <i>C</i>2/<i>m</i> phase in Li<sub><i>x</i></sub>(Li<sub>δ</sub>Co<sub>1−δ</sub>)ÂO<sub>2−δ</sub> is found to appear in the limited <i>x</i> and <i>T</i> ranges. The characteristics and possible origin of <i>T</i><sub>s1</sub> and <i>T</i><sub>s2</sub> for both
stoichiometric Li<sub><i>x</i></sub>CoO<sub>2</sub> and
lithium overstoichiometric Li<sub><i>x</i></sub>(Li<sub>0.02</sub>Co<sub>0.98</sub>)ÂO<sub>1.98</sub> samples are discussed
Factors associated with colonic diverticulosis on multivariate analysis.
<p><sup>*</sup> 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