Specific Heat Measurement under High Pressure

Specific Heat Measurement under
Pressure
• A. Demuer et al., J. Low Temp. Phys. 120 (2000) 245.
• H. Kubo et al., J. Phys. Soc. Jpn. 76 (2007) Suppl. A, p. 221.
Shimizu-Group
M1 Tanaka Shigeki
Contents
 Introduction
• Specific Heat
• Specific Heat under Pressure
• AC-Calorimetric Measurement
 Experimental Method, Results and Discussion
• Experimental Method 1
• Experimental Method 2
• Our Group’s Experiment
 Summary
Specific Heat
heat capacity [C (J/K)]
※ Heat capacity per unit mass is
‘specific heat’.
C = dQ/dT
heater
dQ
sample
T
T + dT
thermometer
Specific heat shows characteristic behavior for various phase transitions !
Example of Experiment
under pressure
 Experimental method : adiabatic method (断熱法)
But adiabatic method under pressure has some difficulties.
Journal of Magnetism and Magnetic Materials 310 (2007) 340–342
Specific Heat (under pressure)
Heat insulation of a sample under pressure is difficult.
dQ = dQ1 + dQ2 +…
Pressure
heater
dQ
sample
T
dQ1
T + dT
dQ2
It is impossible to measure only sample’s specific heat directly.
ac-calorimetric method (交流比熱法)
thermometer
AC-Calorimetric Measurement
The sample is not need to be isolated from the heat bath.
P=P0eiωt
CS
CH
heat capacity : C = CS (Cθ,
CH << CS )
Cθ
K (thermal conductance : 熱伝導度)
Heat bath (refrigerator)
1. give ac power P=P0eiωt to the sample
2. The sample vibrates with amplitude Tac=│P0/(K+iCω)│.
3. measure Tac = P0/(Cω) ( cut off frequency : ω > ω1(=K/C) )
thermal amplitude
thermometer
Cθ
C
sample
S
CH
heater
Tac= P0/(Cω)
Experimental Method 1
• sample : CeRu2Ge2 (200×200×70 μm3)
• heater : Ar laser
• thermocouple : Au-AuFe(0.07%)
• pressure medium : solid 4He
• anvil culet : 1 mm
Results & Discussion 1
 Merits
• use laser for heating and pressure determination → simplify the sample space
• diamond anvil → experiment with observing the sample
• measure the only sample’s specific heat
 Demerits
• laser heating → steady heating of the only sample is difficult
can’t get the absolute value of sample’s specific heat
Experimental Method 2
Thermometer
• sample : Sn (3mg)
• thermometer, heater : RuO2-chip resistor
• pressure medium : In (4 mg)
• anvil culet : 5 mm
Results & Discussion 2
3.5 GPa
 Merits
• Joule heating → steady heating of the sample
• heat the sample with the gasket
• possible to measure the absolute value of the specific heat
 Demerits
• impossible to measure the specific heat of the only sample
• impossible to measure the electric resistivity
Our Group’s Experiment
100 mm
thermocouple
(Au-AuFe(0.07%))
thermocouple
• sample : PrRu4P12
• pressure medium : Daphne 7373 oil
• manometer : ruby
• heat method : Joule heating
A. Miyake, Doctoral thesis (Osaka University) (2007)
Summary
1. Specific heat could be measured under pressure by accalorimetric measurements.
2. Introduced two experiments have each merit and demerit.
3. It is difficult to measure absolute value of only sample’s
specific heat by ac-calorimetric method.
4. A goal of this method is to be performed under higher
pressure.

Download Report