A good pressure-transmitting medium (PTM):

• Provides hydrostatic or quasi-hydrostatic conditions over the pressure and temperature range of your experiment.
• It is chemically inert.
• It is easy to load.

Selecting the “best” PTM depends also on the experimental technique used:

• X-Ray diffraction – The medium needs to have low stress gradients over the intended pressure range to ensure accurate lattice parameter determination.
• Raman & IR Spectroscopy – The medium needs to be transparent or have minimal spectral interference with the sample.
• Electrical Transport & Magnetism – The medium must not interact with the micro-electrodes or the sample.

• Alcohol mixtures – 4:1 Methanol–Ethanol, 16:3:1 Methanol- Ethanol- Water; 1:1 iso-Pentane, 5:1 iso-Pentane
• Mineral Oils – Silicone, Daphne 7373, 7474, 7575 (and even these days 7676) (*),  Nujol
• Fluorinert liquids – 1:1 FC84- FC87 Fluorinert
• Soft Solids  – NaCl, KBr, CsI
• Gas – Nitrogen, Argon, Neon, Helium

(*) Almax easyLab can only provide Daphne 7373.

At low temperatures (cryogenic conditions), the primary challenge is solidification. Most media freeze or undergo a “glass transition,” which can create massive pressure gradients and apply shear stress that can crush delicate samples or snap microscopic electrical leads.

For high-temperature experiments, the criteria for choosing a good PTM change.

Hydrostaticity remains important, but thermal insulation and chemical inertness become the top priorities. Without a proper medium, the heat from your sample will conduct directly into the diamond anvils, potentially causing them to oxidize, graphitize, or crack.

Selecting an appropriate pressure medium is highly subjective. In addition to its hydrostaticity, other factors—such as transparency, chemical inertness, and compatibility with both the sample and the experimental conditions—must also be taken into account. The pressures listed on this page and in the summary table below should therefore be considered as general guidelines.

The references listed below are recommended for more detailed explanations and details:

2007 – Angel, J. Ross et al – Effective hydrostatic limits of pressure media for high-pressure crystallographic studies

2009 – Klotz, Stefan et al  – Hydrostatic Limits of 11 Pressure Transmitting Media

2009 – Tateiwa, Naoyuki and Haga, Yoshinori  – Evaluations of pressure-transmitting media for cryogenic experiments with diamond anvil cell

2012 -  Loveday, John – High-Pressure Physics

2019 – Celeste, A et al – Hydrostaticity of pressure-transmitting media for high pressure infrared spectroscopy