بررسی تاثیر آلایش یون sm3+ بر ویژگی‌های پیزوالکتریکی سرامیک‌های pin-pmn-pt

مواد پیزوالکتریک به صورت گسترده ای در کاربردهای مرتبط با تبدیل انرژی الکتریکی به مکانیکی (و برعکس) مانند حسگرها و مبدل های الکترومکانیکی به کار می روند. در میان مواد پیزوالکتریک، ترکیبات فروالکتریک خانواده ی relaxor-pt به دلیل نشان دادن ویژگی‌های پیزوالکتریکی عالی توجه زیادی به خود جلب کرده اند. در این مقاله تاثیر آلایش ساماریوم بر ویژگی‌های ساختاری و پیزوالکتریکی پیزوسرامیک های pin-pmn-pt با فرمول شیمیایی 26[pb(nb1/2in1/2)o3]-40[pb(mg1/3nb2/3)o3-34pbtio3 بررسی شده است. نتایج بدست آمده از الگوی xrd نشان داد که نمونه ها دارای ساختار بلوری پروسکایتی به صورت تک فاز هستند. نمودار حلقه ی پسماند الکتریکی نمونه ها نشان داد که آلایش ساماریوم سبب افزایش میدان وادارندگی و کاهش قطبش پسماند نمونه ها می گردد. نتایج اندازه گیری ثابت دی الکتریک بر حسب دما نشان داد که دمای کوری نمونه ها با افزایش غلظت آلایش، کاهش می یابد. نمونه ی شامل 1% آلایش ساماریوم دارای بیشترین مقادیر ثابت دی الکتریک نسبی (er=4370)، ضریب بار پیزوالکتریک (d33=695 pc/n) و ضریب جفت‌شدگی الکترومکانیکی موثر (kp=52%) بود. مقدار d33 این نمونه در مقایسه با پیزوسرامیک‌های مرسوم خانواده‌ی pzt مقدار بزرگی است.

investigation of the effect of sm3+ doping on the piezoelectric properties of pin-pmn-pt ceramics

1. introductionpiezoelectric materials, capable of generating voltage under mechanical stress (and vice versa), are crucial in various industries like medical, military, electronics, and automotive applications. they include ceramics, polymers, and single crystals, with high-performance types like the relaxor-pt family that offer high piezoelectric coefficients. while single crystals provide exceptional properties, their high-cost limits widespread use. recent research shows that doping the relaxor-pt ferroelectrics with elements such as samarium can dramatically enhance their piezoelectric response (raising the d33 coefficient from around 360 to 1500 pc/n for pmn-pt). the current study examines the effect of sm3+ doping on pin-pmn-pt near the morphotropic phase boundary, where the coexistence of different crystal phases results in maximum electrical response. 2. methodologysm-doped pin-pmn-pt ceramics (26[pb(nb1/2in1/2)o3]-40[pb(mg1/3nb2/3)o3-34pbtio3] with 0-3 mol% sm) were synthesized using a two-step solid-state method. high-purity oxide precursors were first calcined to form intermediate compounds (innbo₄ and mgnb₂o₆ at 1100°c), then mixed with sm₂o₃, pbo, and tio2, recalcined at 850°c, and sintered into pellets at 1200°c. the resulting samples were characterized through xrd for phase analysis, coated with silver electrodes, poled under an electric field, and evaluated for dielectric and piezoelectric properties using an lcr-meter (hioki im3570) and a d33-meter (poly-k4000), demonstrating a systematic investigation of sm doping effects on this relaxor ferroelectric system. 3. results and discussionthe xrd analysis revealed that all sm-doped pin-pmn-pt samples maintained a perovskite structure, though sm-2 and sm-3 exhibited minor pyrochlore phase formation, attributed to nb-rich regions arising from charge imbalance when sm3+ substitutes for smaller pb2+ at a-sites. the (200) peak's shift toward higher angles confirmed sm3+ incorporation, while its broad, unsplit profile suggested a mixed-phase (rhombohedral + tetragonal) coexistence near the morphotropic phase boundary. the p-e loops demonstrate that increasing sm3+ doping concentration induces hardening effects in the pin-pmn-pt ceramics, evidenced by widening loops and a systematic increase in coercive field (ec). this hardening behavior stems from two key mechanisms: (1) a sm3+-driven phase evolution toward tetragonal symmetry, where 90° domain walls require higher switching energy compared to rhombohedral 180° walls, and (2) reduced remnant polarization (pr) due to weakened pb-o hybridization from a-site pb2+ substitution. the complementary trends in ec (↑) and pr (↓) underscore the critical trade-off between coercivity and polarization in rare-earth-modified relaxor ferroelectrics. the temperature-dependent dielectric properties of sm: pin-pmn-pt ceramics reveal three key effects of samarium incorporation: (1) the dielectric constant (εᵣ) peaks at the curie temperature (tc), showing characteristic relaxor ferroelectric behavior with a broad transition. (2) sm doping elevates εᵣ by flattening the free energy profile through induced polar nanoregions (pnrs), while simultaneously reducing tc (from ~185°c to ~160°c for 0-3% sm) due to weakened pb-o hybridization and spontaneous polarization. (3) the modified curie-weiss analysis confirms enhanced relaxor behavior with doping, as sm promotes pnr dynamics through a-site disorder, explaining both the dielectric enhancement and transition broadening. these results highlight sm's dual role as a modifier of both macroscopic properties (tc, εᵣ) and nanoscale domain structure in relaxor ferroelectrics. the planar electromechanical coupling coefficient (kp) was calculated from the impedance diagram. in the resonant state, the piezoelectric component effectively converts electrical energy into mechanical vibrations. the dominant response at this point is capacitive. in this case, the device stores electrical energy in an electric field like a capacitor. in the anti-resonance state, the device behaves more like an inductor due to mechanical damping effects and dissipates electrical energy as heat. it is observed that the highest kp value of 52% was obtained for the sample doped with 1% sm. the d33 of the samples was measured at room temperature. the d33 value increases with increasing samarium concentration up to 1% and then decreases. the highest d33 value of 695 pc/n was obtained for the sample doped with 1% sm. this value is larger than the values reported for the pzt family compounds (200