Pressure alters the nature of chemical bonds and triggers novel reactions. Here, we employed first-principles calculations combined with the CALYPSO structural search technique to reveal the charge transfer reversal between Ca and Te under high pressure in the calcium-tellurium compound (CaxTe1-x, x = 1/4, 1/3, 1/2, 2/3). We predict several new phases with conventional and unconventional compounds and found an unfamiliar phenomenon: the Ca-Te compounds will reverse charge transfer between Ca and Te atoms and decompose into elemental solids under pressure. The Bader charge analyses indicate that the Ca2+ ion gains electrons and becomes an anion under high pressure. This leads to a weakened electrostatic interaction between Ca and Te and ultimately results in decomposition. The calculated band occupation number suggests that the occupation of Ca 3d orbitals under high pressure corresponds to this atypical phenomenon. Our results demonstrated the reverse charge transfer between Ca and Te and, in addition, clarified the mechanism of CaxTe1-x decomposition into solid Ca and Te elements under high pressure, providing important insights into the evolution of the properties of alkaline-earth chalcogenide compounds under high pressure.
This work utilized first-principles calculations and the CALYPSO structure search technique to systematically investigate the crystal structure stability of CsxIy compounds under high pressures ranging from 0 to 500 GPa. Several new phases with both conventional and unconventional stoichiometries were predicted. Interestingly, we discovered a counter-intuitive phenomenon where Cs-I compounds decompose into Cs and I elemental solids under pressure. To understand the physical mechanism behind this pressure-induced decomposition, we examine the phenomenon from two distinct perspectives: enthalpy of formation and interatomic interactions. Our results suggest that the main cause is the weakening of electrostatic interactions leading to the decomposition, while the weak covalent interaction plays a minor role. From an energy perspective, the decrease in the formation of enthalpy (ΔH) is primarily due to a reduction in the difference of internal energy (ΔU). These findings provide valuable insights into the decomposition mechanism and high-pressure properties of alkali metal halides. The counterintuitive phenomenon of high-pressure charge transfer and decomposition may inspire new ideas and perspectives in the fields of geology and the study of alkali metal halides under extreme conditions.
External mechanical stress alters the nature of chemical bonds and triggers novel reactions, providing interesting synthetic protocols to supplement traditional solvent- or thermo-based chemical approaches. The mechanisms of mechanochemistry have been well studied in organic materials made of a carbon-centered polymeric framework and covalence force field. They convert stress into anisotropic strain which will engineer the length and strength of targeted chemical bonds. Here, we show that by compressing silver iodide in a diamond anvil cell, the external mechanical stress weakens the Ag-I ionic bonds and activate the global diffusion of super-ions. In contrast to conventional mechanochemistry, mechanical stress imposes unbiased influence on the ionicity of chemical bonds in this archetypal inorganic salt. Our combined synchrotron X-ray diffraction experiment and first-principles calculation demonstrate that upon the critical point of ionicity, the strong ionic Ag-I bonds break down, leading to the recovery of elemental solids from a decomposition reaction. Instead of densification, our results reveal the mechanism of an unexpected decomposition reaction through hydrostatic compression and suggest the sophisticated chemistry of simple inorganic compounds under extreme conditions.
OBJECTIVES: This study aimed to determine the relationship between the polymorphisms of the H1/H2 gene of platelet membrane receptor P2Y12 and cerebral infarction (CI) in a Han population in North Shandong Province, People's Republic of China. PATIENTS AND METHODS: A case-control study, which involved 168 nonstoke subjects (contrast group) and 152 CI patients (CI group), was conducted. The state of subjects in the CI group was validated by computed tomography or MRI. The clinical data were categorized into two groups. The data included age, gender, smoking, drinking, shrinkage pressure, diastolic blood pressure, blood glucose, cholesterol, triglyceride, low-density lipoprotein, high-density lipoprotein, serum uric acid, fibrinogen and homocysteine. The polymorphisms were genotyped with PCR and restriction fragment length polymorphism analysis. The distribution characteristics of nonstoke subjects and CI patients and the relationship between the polymorphisms of the H1/H2 gene of platelet membrane receptor P2Y12 and ischemic stroke were analyzed. RESULTS: No significant difference was found between the contrast group and CI group (P>0.05) in terms of age, gender composition, smoking, alcohol consumption, blood glucose, cholesterol, triglyceride, low-density protein, high-density lipoprotein cholesterol, uric acid and homocysteine. In contrast, significant differences were found between these two groups (P<0.01) in terms of SBP, DBP and plasma fibrinogen level. The genotyping revealed 112 carriers of the wild-type H1/H1 genotype and 40 carriers of the mutational H2 allele of P2Y12 H1/H2 in the CI group and 140 carriers of the wild-type H1/H1 genotype and 28 carriers of the mutational H2 allele of P2Y12 H1/H2 in the contrast group. Furthermore, the H1/H2 and H2/H2 gene frequencies (26.3%) were significantly higher in the CI group (χ2=4.440, P<0.05) than those in the contrast group (16.7%). Moreover, the frequencies of the H2 allele in the CI and contrast groups were 14.5% and 8.6%, respectively, and the difference was statistically significant (χ2=5.392, P<0.05). Multiple logistic regression analysis results revealed that factors associated with CI include systolic blood pressure and plasma fibrinogen level, which carry the -893T gene. After adjusting for potential confounding factors, the H2 allele carriers had a 1.928-fold increased risk for CI (OR=1.928, 95% confidence interval: 1.137-3.188; P=0.038) when compared with noncarriers. CONCLUSION: The present study found that hypertension and elevated plasma fibrinogen levels are significant risk factors for ischemic stroke and confirmed that the H1/H2 and H2/H2 genes of platelet membrane glycoprotein receptor P2Y12 are risk factors of ischemic stroke.
