The epitaxial growth, structural properties, and ferroelectric properties of bismuth lanthanum nickel titanate (Bi1−xLax) (Ni0.5Ti0.5)O3 (BLNT) thin films deposited on Pt(100)∕MgO(100) substrates by rf magnetron sputtering have been investigated using x-ray diffraction, transmission electron microscope, and polarization–electric field hysteresis loop measurements. The ferroelectric BLNT(00ℓ) phase with c-axis orientation and a single-phase tetragonal perovskite structure appeared at x⩾0.3. The tetragonality (c∕a) increased significantly from 1.004 to 1.028 with increasing La content. The fabricated BLNT films of x⩾0.3 indicated the apparent fourfold rotational symmetry observed for a MgO(202) substrate, a bottom Pt(202) electrode, and a BLNT(101) ferroelectric film, based on ϕ scan measurements. These results imply that the present La-substituted BLNT films are grown heteroepitaxially at x⩾0.3. It was confirmed that Bi in the BLNT films is in a trivalent state at A sites in the perovskite crystal, based on x-ray anomalous diffraction measurements and x-ray absorption near edge structure spectra. The sputtering technique using compacted powder targets designed by taking the bond dissociation energy of metal oxides into account provided epitaxial perovskite-structured BLNT thin films on Pt(100)∕MgO(100) substrates. It is shown that the c-axis oriented epitaxial BLNT film exhibits a hysteresis loop shape with a Pr value of 12μC∕cm2 that is comparable to typical high-performance Bi3.25La0.75Ti3O12 (BLT) film.

The epitaxial growth and formation mechanism of the partially La-and Nd-substituted perovskite structures, and the ferroelectric properties of bismuth lanthanoid nickel titanate [(Bi 1Àx La x )(Ni 0:5 Ti 0:5 )O 3 ; BLNT and (Bi 1Àx Nd x )(Ni 0:5 Ti 0:5 )O 3 ; BNNT] based solid solution films deposited on Pt(100)/MgO(100) substrates by rf sputtering have been investigated using X-ray diffraction, transmission electron microscope, and polarization-electric field hysteresis loop measurements. BLNT samples at x ! 0:3 and BNNT samples at x ! 0:4 were confirmed to have a single-phase perovskite structure. This small difference is speculated that it is related to metal-oxygen bond dissociation energy. The sample substituted with La exhibited the best hysteresis loop at x ¼ 0:5 with a remanent polarization of P r ¼ 12 mC/cm 2 and the sample substituted by Nd exhibited the best hysteresis loop at x ¼ 0:4 with a remanent polarization of P r ¼ 2 mC/cm 2 .

After depositing amorphous (Bi0.5La0.5)(Ni0.5Ti0.5)O3 (BLNT) films on BLNT seed layer/Pt(100)/ MgO(100) substrates by room-temperature sputtering, the crystallization of the perovskite-struc- tured films has been tried by hot isostatic pressing (HIP). The samples with a single-phase perovskite structure HIP-treated at 800°C for 1 h under gas pressures of 0.51.0 MPa showed good crystallinity of  = 0.960.98 without accompanying the precipitation of the secondary phase. It was confirmed that a large root mean square roughness value of 44.2 nm for the sample HIP-treated at 800°C for 1 h under gas pressure of 0.1 MPa is due to innumerable Bi4Ti3O12-like rod-shaped grains precipitated in the film surface, based on atomic force microscopy. It is shown that the BLNT sample HIP-treated at 800°C for 1 h under gas pressure of 1.0 MPa exhibits the best hysteresis loop shape with a remanent polarization of Pr = 5 C/cm2 and a coercive field of Ec = 150 kV/cm of the six.

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