Lead-free 0.94NBT-0.06BT-xLa ceramics at x = 0.0-1.0 (%) were synthesized by a conventional solid-state route. XRD shows that the compositions are at a morphotropic phase boundary where rhombohedral and tetragonal phases coexist. With increasing La 3+ content pyroelectric coefficient (p) and figures of merits greatly increase; however, the depolarization temperature (Td) decreases. p is 7.42 x 10-4 C.m-2 .°C-1 at RT at x=0.5% and 105.4 x10-4 C.m-2 °C-1 at Td at x=0.2%. Fi and Fv show improvements at RT from 1.12 (x=0%) to 2.65 (x10-10 m.v-1) (x=0.5%) and from 0.021 to 0.048 (m 2 .C-1) respectively. Fi and Fv show a huge increase to 37.6 x10-10 m.v-1 and 0.56 m2.C-1 respectively at Td at x=0.2%. FC shows values of 2.10, 2.89, and 2.98 (x10-9 C.cm-2. °C-1) at RT at 33, 100 and 1000 (Hz) respectively. Giant pyroelectric properties make NBT-0.06BT-xLa at x=0.2% and 0.5% promising materials for many pyroelectric applications.

La and Ta co-doped Lead-free 0.94NBT-0.06BT ceramics were synthesized by a conventional solid-state route. The compositions remain at a morphotropic phase boundary. The depolarization temperature (Td) decreased with increasing doping contents. The room temperature (RT) pyroelectric coefficient (p) was highly enhanced compared with undoped material (3.15 x10-4 C.m-2 .°C-1) and reached 12.9 x10-4 C.m-2 .°C-1 , whereas, at Td, 58.6 x10-4 C.m-2 .°C-1 could be obtained rather than 23.9 x10-4 C.m-2 .°C-1 for undoped materials. The pyroelectric figure of merits, Fi and Fv, also showed a huge improvement from 1.12 x10-10 m.v-1 and 0.021 m 2 .C-1 of undoped material to 4.61 x10-10 m.v-1 and 0.078 m 2 .C-1 of doped materials at RT, and to 20.94 x 10-10 m.v-1 and 0.28 x10-10 m 2 .C-1 at Td. RT FC values are2 .40, 2.46, and 2.57 (x10-9 C.cm-2 .°C-1) at frequency 33, 100 and 1000 (Hz) respectively, at La = Ta = 0.2 %. The pyroelectric coefficient achieved at RT in this study is almost one order of magnitude higher than PZT materials, furthermore, the figure of merits of the new compositions are comparable with or even better in those of PZT materials and other leadfree ceramics. The improvement in the pyroelectric properties makes La and Ta co-doped NBT-0.06BT ceramics possible materials to replace lead-containing PZT ceramics for infrared detector materials at a wide temperature range.

Ta-doped lead-free 0.94NBT-0.06BT-xTa (x = 0.0-1.0 %) ceramics were synthesized by a conventional solid-state route. XRD shows that the compositions are at a morphotropic phase boundary where rhombohedral and tetragonal phases coexist. The depolarization temperature (Td) shifted to lower temperature with the increase of Ta content. The pyroelectric coefficient (p) of doped ceramics greatly enhanced compared with undoped material and reached a maximum of 7.14 x10-4 C.m-2. °C-1 at room temperature (RT) and 146.1 x10-4 C.m-2 °C-1 at Td at x = 0.2%. The figure of merits, Fi and Fv, also showed a great improvement from 1.12 x10-10 m.v-1 and 0.021 m 2 .C-1 at x = 0.0 to 2.55 x10-10 m.v-1 and 0.033 m 2 .C-1 at x = 0.2% at RT. Furthermore, Fi and Fv show the huge improvement to 52.2 x 10-10 m.v-1 and 0.48 x10-10 m.v-1 respectively at Td at x = 0.2%. FC shows a value between 2.26 to 2.76 x10-9 C.cm-2. °C-1 at RT at x= 0.2%. The improved pyroelectric properties make NBT-0.06BT-0.002Ta ceramics a promising infrared detector material.

Lead-free 0.94Na 0.5 Bi 0.5 TiO 3 -0.06Ba 1?x TiO 3 (NBT-0.06B 1?x T) ceramics (0.0 B x B 0.03) were synthesized by a conventional solid-state reaction process. X-ray diffraction shows that the compositions are at the morphotropic phase boundary where rhombohedral and tetragonal phase coexist. Grain size slightly changes with the increase of Ba 2? content and reaches the minimum at x = 0.02. The depolarization temperature (T d ) decreases with the extra Ba 2? content but the lowest T d was obtained at x = 0.01-0.02. The pyroelectric coefficient (p) was measured as a function of Ba 2? content, and increased from 2.90 9 10 -4 to 3.54 9 10 -4 C m -2°C-1 , and from 55.3 9 10 -4 to 740.7 9 10 -4 C m -2°C-1 for x = 0.00 and 0.02 at RT, and depolarization temperature (T d ) respectively. The pyroelectric coefficient (p) shows a large increase with rising the temperature and reaches the maximum value at the depolarization temperature (T d ). The figures of merits of F i , F v and F D have all been improved with the addition of extra barium. These improved pyroelectric properties indicate that NBT-0.06B 1?x T is a promising material for pyroelectric applications or a wide range of temperature.

Nonstoichiometry lead-free 0.94Na x Bi y TiO 3 -0.06Ba z TiO 3 (N x B y T-0.06B z T) (from x = y = 0.5, z = 1.00 to x = 0.5, y = 0.534, z = 1.02) ceramic compositions were prepared by a conventional solid-state route. XRD shows that the compositions are at a morphotropic phase boundary where rhombohedral and tetragonal phases coexist. The depolarization temperature (T d ) can be lowered by modifying x, y and z. The pyroelectric coefficient (p) of nonstoichiometry N x B y T-0.06B z T compositions is greatly increased, compared with stoichiometry NBT-0.06BT composition, from 3.15 9 10 -4 C m -2°C-1 at room temperature (RT) and 23.9 9 10 -4 C m -10 m v -1 , 0.39 9 10 -10 m 2 C -1 and 138.7 9 10 -6 Pa -1/2 , respectively, at T d . The same composition also presents F C values which are *2.58 and *2.86 (910 -9 C cm -2°C-1 ) at RT at 100 and 1000 (Hz). N 0.5 B 0.534 T-0.06BT and N 0.5 B 0.534 T-0.06B 1.02 T compositions show a large p values at a wide temperature range. The enhanced pyroelectric properties make nonstoichiometry N 0.52 B 0.52 T-0.06BT composition a promising candidate for pyroelectric and other applications at wide temperatures range.