Comprehending the
oxygen vacancy distribution in oxide ion conductors
requires structural insights over various length scales: from the
local coordination preferences to the possible formation of agglomerates
comprising a large number of vacancies. In Y-doped ceria,
89
Y NMR enables differentiation of yttrium sites by quantification
of the oxygen vacancies in their first coordination sphere. Because
of the extremely low sensitivity of
89
Y, longer-range information
was so far not available from NMR. Herein, we utilize metal ion-based
dynamic nuclear polarization, where polarization from Gd(III) dopants
provides large sensitivity enhancements homogeneously throughout the
bulk of the sample. This enables following
89
Y–
89
Y homonuclear dipolar correlations and probing the local
distribution of yttrium sites, which show no evidence of the formation
of oxygen vacancy rich regions. The presented approach can provide
valuable structural insights for designing oxide ion conductors.
The lattice dynamics of organic semiconductors has a significant role in determining their electronic and mechanical properties. A common technique to control these macroscopic properties is to chemically modify the molecular structure. These modifications are known to change the molecular packing, but their effect on the lattice dynamics is relatively unexplored. Therefore, we investigate how chemical modifications to a core [1]benzothieno-[3,2-b]benzothiophene (BTBT) semiconducting crystal affect the evolution of the crystal structural dynamics with temperature. Our study combines temperature-dependent polarization-orientation (PO) low-frequency Raman measurements with first-principles calculations and single-crystal X-ray diffraction measurements. We show that chemical modifications can indeed suppress specific expressions of vibrational anharmonicity in the lattice dynamics. Specifically, we detect in BTBT a gradual change in the PO Raman response with temperature, indicating a unique anharmonic expression. This anharmonic expression is suppressed in all examined chemically modified crystals (ditBu-BTBT and diC8-BTBT, diPh-BTBT, and DNTT). In addition, we observe solid−solid phase transitions in the alkyl-modified BTBTs. Our findings indicate that π-conjugated chemical modifications are the most effective in suppressing these anharmonic effects.
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