5 Mössbauer Spectroscopy with High Spatial Resolution …
247
obtain additional information about the electronic environment around the nucleus
[102–108]. Determination of hyperfine parameter variations are especially crucial
for identifying spin and structure transitions in the non-magnetic state. Key to all
studies listed in Table 5.3 is that energy domain Mössbauer spectra can usually be
deconvoluted uniquely into individual components.
Studies carried out by geoscience laboratories generally address research questions beyond observing material behaviour of geologically relevant phases at high
pressure. For example, spin transitions can change density and elastic properties
[109] which can be used to interpret seismic anomalies [110]. Phase transitions can
involve chemical transformation as well as structural and electronic changes [111].
Deciphering the chemistry of Earth’s core relies on knowledge of phase relations
involving iron and potential light alloying elements [112, 113]. Finally, high-pressure
studies of meteorites provide information on impact processes that occurred in their
history [114–116].
5.6.2 In Situ High-Pressure Studies with a Synchrotron
Source
The advent of nuclear resonance beam lines at third-generation synchrotron sources
greatly expanded possibilities for in situ high-pressure Mössbauer studies on geological materials. The smaller beam size and higher flux enabled studies at a wider range
of pressures, dramatically shorter counting times made combined high-temperature
high-pressure measurements possible, and generous access programmes expanded
the user base to include those without in house facilities. The result is a wider range
of research topics addressed, where studies focussed exclusively on high-pressure
phase transitions make up only 32% of the total number of publications [19, 28, 29,
40, 117–139] (Table 5.4).
Other studies reported in Table 5.4 also involve phase transitions, but address
research questions related to Earth properties. For example, a large number of studies
focus on the chemistry of Earth’s core, since phase transitions change properties such
as density and sound velocity [140–148]. These can be compared with bulk geophysical measurements (for example from seismology) to place constraints on which
elements could be alloyed with iron in Earth’s core. Other studies focus on properties of Earth’s mantle, in particular elastic properties [149–161] and how velocity
anomalies observed by seismology can be explained [162–167]. Iron oxidation state
influences mantle chemistry, both in the present day and throughout Earth’s history
[18, 168–172]. Determination of electronic structure and crystal chemistry of mantle
minerals at high pressure can place constraints on their behaviour in Earth’s mantle
[173–180], and studies of magnetic properties provide insight into planetary magnetic
fields [181].
Research questions addressed by high-pressure Mössbauer studies also target
dynamic processes in Earth’s interior. For example, spin transitions can change
247
obtain additional information about the electronic environment around the nucleus
[102–108]. Determination of hyperfine parameter variations are especially crucial
for identifying spin and structure transitions in the non-magnetic state. Key to all
studies listed in Table 5.3 is that energy domain Mössbauer spectra can usually be
deconvoluted uniquely into individual components.
Studies carried out by geoscience laboratories generally address research questions beyond observing material behaviour of geologically relevant phases at high
pressure. For example, spin transitions can change density and elastic properties
[109] which can be used to interpret seismic anomalies [110]. Phase transitions can
involve chemical transformation as well as structural and electronic changes [111].
Deciphering the chemistry of Earth’s core relies on knowledge of phase relations
involving iron and potential light alloying elements [112, 113]. Finally, high-pressure
studies of meteorites provide information on impact processes that occurred in their
history [114–116].
5.6.2 In Situ High-Pressure Studies with a Synchrotron
Source
The advent of nuclear resonance beam lines at third-generation synchrotron sources
greatly expanded possibilities for in situ high-pressure Mössbauer studies on geological materials. The smaller beam size and higher flux enabled studies at a wider range
of pressures, dramatically shorter counting times made combined high-temperature
high-pressure measurements possible, and generous access programmes expanded
the user base to include those without in house facilities. The result is a wider range
of research topics addressed, where studies focussed exclusively on high-pressure
phase transitions make up only 32% of the total number of publications [19, 28, 29,
40, 117–139] (Table 5.4).
Other studies reported in Table 5.4 also involve phase transitions, but address
research questions related to Earth properties. For example, a large number of studies
focus on the chemistry of Earth’s core, since phase transitions change properties such
as density and sound velocity [140–148]. These can be compared with bulk geophysical measurements (for example from seismology) to place constraints on which
elements could be alloyed with iron in Earth’s core. Other studies focus on properties of Earth’s mantle, in particular elastic properties [149–161] and how velocity
anomalies observed by seismology can be explained [162–167]. Iron oxidation state
influences mantle chemistry, both in the present day and throughout Earth’s history
[18, 168–172]. Determination of electronic structure and crystal chemistry of mantle
minerals at high pressure can place constraints on their behaviour in Earth’s mantle
[173–180], and studies of magnetic properties provide insight into planetary magnetic
fields [181].
Research questions addressed by high-pressure Mössbauer studies also target
dynamic processes in Earth’s interior. For example, spin transitions can change