研究目的
To investigate the lattice dynamics and negative thermal expansion behavior in the framework compound ZnNi(CN)4, which contains metals in both 2D and 3D local environments, using inelastic neutron scattering and ab initio calculations.
研究成果
ZnNi(CN)4 exhibits pronounced negative thermal expansion driven by low-energy phonon modes, including rigid-unit modes and additional twisting motions due to the 2D coordination of Ni in a 3D framework. The ab initio model validated by INS provides insights into the dynamics, suggesting that lower structural constraints can enhance NTE but may affect crystallinity.
研究不足
The sample was poorly crystalline, making refinement of unit-cell parameters impossible. The quasiharmonic approximation may not fully capture explicit anharmonic effects at higher temperatures. The study was limited to temperatures up to 400 K and did not include pressure-dependent measurements.
1：Experimental Design and Method Selection:
The study combined experimental inelastic neutron scattering (INS) measurements with ab initio lattice dynamical calculations to probe phonon dynamics and thermal expansion. The quasiharmonic approximation (QHA) was used for thermal expansion calculations.
2：Sample Selection and Data Sources:
A 2-g powdered sample of ZnNi(CN)4 was synthesized via precipitation from aqueous solutions of K2Ni(CN)4·nH2O and Zn(NO3)2·6H2O. Data were collected using neutron and x-ray diffraction, IR and Raman spectroscopy.
3：2O. Data were collected using neutron and x-ray diffraction, IR and Raman spectroscopy. List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Equipment included a Quantachrome micropycnometer for density measurement, Perkin Elmer Spectrum 100 spectrometer for IR, Renishaw InVia Raman microscope for Raman, Bruker D8 diffractometer for XRD, GEM diffractometer at ISIS for neutron diffraction, and IN6 spectrometer at ILL for INS. Materials included K2Ni(CN)4·nH2O (Aldrich), Zn(NO3)2·6H2O (BDH), distilled water, helium gas, aluminium container, quartz capillary.
4：Experimental Procedures and Operational Workflow:
The sample was synthesized, dried, and characterized. INS measurements were performed at 200, 300, and 400 K with an incident wavelength of 4.14 ?. Data reduction involved background subtraction, multiphonon correction, and calculation of generalized phonon density-of-states.
5：14 ?. Data reduction involved background subtraction, multiphonon correction, and calculation of generalized phonon density-of-states. Data Analysis Methods:
5. Data Analysis Methods: Data were analyzed using the LAMP program for INS data reduction. Phonon calculations used VASP and PHONOPY software. Mode Grüneisen parameters and thermal expansion coefficients were derived from ab initio calculations under QHA.
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spectrometer
Spectrum 100
Perkin Elmer
Measuring IR frequencies.
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diffractometer
D8
Bruker
Collecting powder x-ray diffraction data in transmission mode with Cu Kα1 radiation.
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micropycnometer
Quantachrome
Measuring sample density at room temperature using helium gas.
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Raman microscope
InVia
Renishaw
Measuring Raman frequencies with excitation wavelength of 785 nm.
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diffractometer
GEM
ISIS Neutron and Muon Source
Collecting total neutron diffraction data over a wide-angle range.
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spectrometer
IN6
Institut Laue-Langevin
Performing inelastic neutron scattering measurements with high resolution.
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cryofurnace
orange
Cooling the sample for INS measurements.
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software
LAMP
ILL
Data reduction and treatment for INS measurements.
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software
VASP
Vienna ab initio simulation package
Performing ab initio calculations for lattice dynamics.
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software
PHONOPY
Calculating phonon density-of-states and mode Grüneisen parameters.
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