Energy Functional Materials Engineering Laboratory

1st alumni meeting of Nagasaki-Yamada lab. was held on Nov. 23rd.

On Jul. 18, Prof. Guorong Li (Shanghai Institute of Ceramics) visited us and lectured on high-entropy ferroelectric ceramics. In addition, Dr. Lei Meng and Dr. Xueyou Yuan gave their seminars.

1) Fabrication and Properties of ABO₃ Ferroelectric Ceramics with A- and B-site disorder for high-energy storage (Prof. Guorong Li)
2) Strong Second-order Nonlinear-polarization in Widegap ZnMgO Thin-films with Li Incorporation (Dr. Lei Meng)
3) Extraordinarily Large Extrinsic Contribution Ratio to Piezo-response in Monoclinic (K, Na)NbO₃ Epitaxial Films (Dr. Xueyou Yuan)

Our collaborative paper with Kyoto University entitled “Ferroelectric Freestanding Hafnia Membranes with Metastable Rhombohedral Structure down to 1-nm-thick” has been published in Nat. Commun. We fabricated stable 1-nm-thick hafnia membranes exhibiting the metastable rhombohedral structure and out-of-plane ferroelectric polarizations as large as 13 μC/cm².

Citation: NC 15, 1055196 (2024).

On Jun. 6, Dr. Alexandros Emborasa (ETH Zurich) visited us and lectured on neuromorphic computing.

Lecturer: Dr. Alexandros Emborasa (ETH Zurich)
Seminar title: Neuromorphic Computing: From Devices to Applications

Our paper entitled “Novel Route for Enhancing Piezoelectricity of Ferroelectric Films: Controlling Nontrivial Polarization States in Pb(Zr, Ti)O₃ Monodomain Superlattice Structure” has been published in ACS Appl. Mater. Interfaces. We found that (111)-epitaxial artificial superlattice thin films consisting of Pb(Zr_0.4Ti_0.6)O₃ and Pb(Zr_0.6Ti_0.4)O₃ can be stabilized into unique monodomain state, which results in the piezoelectric response larger than the typical clamped films with the same chemical compositions.

Citation: ACSAMI 16, 16145 (2024).

Our paper entitled “Extraordinarily Large Contribution Ratio of Ferroelastic Domain Switching to Piezoresponse in Monoclinic (K, Na)NbO₃ Films” has been published in Adv. Electron. Mater. We found that the extrinsic contribution to the piezoresponse in (111)epitaxial monoclinic (K, Na)NbO₃ films is extraordinarily large, over 100% under moderate electric fields.

Citation: AEM 10, 2300405 (2024).

Our paper entitled “Dynamic Electrical Response of Vortex Polarization in (Pb_0.9Sr_0.1)TiO₃/SrTiO₃ Artificial Superlattice Thin Films” has been published in Appl. Phys. Lett. We found that the reorientation of dipole moments in the vortex domains is susceptible to the applied electric field pulses of 500 μs and is a reversible process. Although the centrosymmetric vortex domain structure is not considered to exhibit piezoelectricity, an evident change in the out-of-plane lattice constant with the applied electric field was revealed.

Citation: APL 121, 172904 (2022).

Our paper entitled “Strong Electro-optic Effect in Mg Incorporated ZnO Thin Films” has been published in Appl. Phys. Lett. We found that the Mg incorporation enhances the linear EO response significantly. In particular, the Zn_0.72Mg_0.28O thin film showed an effective EO coefficient of 7.6 pm/V, which is over three times larger than the reported values for ZnO-based thin films and over twice larger than that of ZnO single crystals. This study is the collaborative research with Dr. Meng of Institute of Semiconductors, Chinese Academy of Sciences.

Citation: APL 121, 152903 (2022).

Our paper entitled “Effect of Ni Doping on the Electro-optic Property in K(Ta_0.6Nb_0.4)O₃ Films” has been published in Jpn. J. Appl. Phys. We found that a larger withstand electric field was achieved by Ni doping, therefore, the variation of refractive index by the applicable maximum electric field was increased.

Citation: JJAP 61, SN1005 (2022).