Two Types of Negative Thermal Expansion Observed in PbCr_1–xTi_xO₃

Abstract

Two negative thermal expansions (NTEs) with different mechanisms were observed in solid solutions of perovskite-type oxides PbCrO3 and PbTiO3. PbCr1–x Ti x O3 was found to adopt a cubic structure the same as that of PbCrO3 for x ≤ 0.6 and a PbTiO3-type tetragonal structure for x ≥ 0.7. The NTE observed at x ≤ 0.6 was accompanied by a cubic-to-cubic phase transition originating from the rearrangement of Pb2+/Pb4+ in a complex local structure called a charge glass. The volume shrinkage of −2.5% observed in PbCrO3 is sufficiently large despite the absence of intermetallic charge transfer, which is the origin of pressure-induced cubic-to-cubic phase transition and 9.8% volume collapse. The NTE in the tetragonal phase was caused by the ferroelectric-to-paraelectric phase transition, the same as in PbTiO3. We succeeded in significantly lowering the working temperature of PbTiO3 as an NTE material by Cr substitution while retaining a large volume shrinkage of 0.6%.

Simultaneous Thermal Enhancement of Upconversion and Downshifting Luminescence by Negative Thermal Expansion in Nonhygroscopic ZrSc(WO4)2PO4:Yb/Er Phosphors

“…Likewise, the confinement within the two-dimensional layered structures may be effective with the energy migration between Ln 3+ dopants for maintaining a high energy transfer efficiency at high temperatures . The different expansion coefficients for lattice parameters may result in a local structural change . Meanwhile, the local structural change of Er 3+ (or Yb 3+ ) may lead to thermally enhanced luminescence.…”

“…23 The different expansion coefficients for lattice parameters may result in a local structural change. 27 Meanwhile, the local structural change of Er 3+ (or Yb 3+ ) may lead to thermally enhanced luminescence. Pure ZSWP has an orthorhombic crystal structure with space group Pnca (No.…”