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In the past 14 years, as a branch of high-entropy alloy (HEA) materials, HEA films and coatings have exhibited the attractive and unique properties, relative to the conventional film and coating materials. The recent research and development of HEA films and coatings are reviewed in this paper. At first, the basic concept of HEAs films and coatings are introduced. Then, their preparation technologies, microstructures and appealing properties are summarized. Moreover, the possible reasons and design criteria for achieving the excellent properties are discussed. Finally, the suggested future research work for the HEA films and coatings are outlined. IMPACT STATEMENT Preparation technologies, microstructures, and properties of HEA films and coatings are reviewed in this paper. The design criteria and suggested research directions are further discussed and proposed.

Pure Bi4Ti3O12 ceramics were prepared using the conventional solid-state reaction method and their dielectric properties were investigated. A dielectric loss peak with the relaxation-type characteristic was observed at about 370K at 100Hz frequency. This peak was confirmed to be associated with the migration of oxygen vacancies inside ceramics. The Cole–Cole fitting to this peak reveals a strong correlation among oxygen vacancies and this strong correlation is considered to commonly exist among oxygen vacancies in ferroelectrics. Therefore, the migration of oxygen vacancies in ferroelectric materials would demonstrate a collective behavior instead of an individual one due to this strong correlation. Furthermore, this correlation is in proportion to the concentration and in inverse proportion to the activation energy of oxygen vacancies. These results could be helpful to the understanding of the fatigue mechanisms in ferroelectric materials.

Polarization and related properties in the M-type lead hexaferrite (PbFe 12 O 19 ) are reported for the first time. The remnant polarization of PbFe 12 O 19 exhibits a maximum value of 104 lC/cm 2 , as well as large spontaneous polarization at room temperature. Annealing of PbFe 12 O 19 in oxygen plays a key role in the saturation of its polarization hysteresis loop because it greatly enhances the ceramic's electric resistance. Two current peaks in the I-V curve reveal a polarization switch, providing effective evidence for the ferroelectricity of PbFe 12 O 19 . Its temperature-dependent dielectric constant undergoes colossal change in the vicinity of two temperatures (322°C and 518°C), which are assigned to the transitions from ferro-to antiferro-and antiferro-to paraelectric phases, respectively. The plots of logarithm of (1/e-1/e m ) as a function of logarithm of (T-T m ) obey a modified Curie-Weiss law, verifying the relaxor ferroelectric characterization of PbFe 12 O 19 . The ceramic also exhibits a strong magnetic hysteresis loop. These combined functional responses of ferroelectricity and ferromagnetism in PbFe 12 O 19 ceramic present an opportunity to create electric devices that actively couple the magnetic and ferroelectric orders.

A three-dimensional homometallic complex [Co(5)(mu(3)-OH)(2)(btec)(2)(bpp)](n) is built from the mixed hydroxide/carboxylate bridged cobalt(ii) chains linked by the 1,2,4,5-benzenetetracarboxylate (btec(4-)) anion and 1,3-bis(4-pyridyl)-propane molecule (bpp). Within each chain, two mu(3)-OH-bridged metal triangles connect to each other by sharing a common vertex to give rise to a bow-tie type Co(5)(mu(3)-OH)(2) subunit, which is joined to adjacent subunits by four mu(1,1)-carboxylate bridges to form a step-like metal-oxygen backbone. The magnetic studies revealed that the coexistence of ferromagnetic and antiferrimagnetic interactions resulted in a ferrimagnetic-like behavior of the homometallic chains. Below a critical temperature (T(N) = 12.5 K), bulk antiferromagnetic ordering was observed at low field due to the weak interchain antiferromagnetic interactions. A metamagnetic transition occurred at a magnetic field of ca. 5 kOe at 2 K.