Effect of uniaxial stress in superprotonic phase transition in Cs3H(SeO4)2

We have carried out the electrical conductivity measurement under the uniaxial stress in the hydrogen-bonded superprotonic conductor Cs3H(SeO4)2. It is found that the increase of the superprotonic phase transition temperature is observed by the uniaxial stress along the b axis at room temperature. On the other hand, no change of phase transition temperature is observed by the uniaxial stress along the c axis. It is also found from the viewpoint of free energy that the value of spontaneous strain a0 in the a–b plane is closely related to the increase of the phase transition temperature under the uniaxial stress. From these results, we deduce that the increase of the superprotonic phase transition temperature by the uniaxial stress is caused by the suppression of the release of the spontaneous strain in the a–b plane.