Impact of ion exchange on vibrational modes in Rb-doped <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>KTiOP</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math>: A R

Recently, ion exchange (IE) has been used to periodically modify the coercive field (<a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msub><a:mi>E</a:mi><a:mi mathvariant="normal">c</a:mi></a:msub></a:math>) of the crystal prior to periodic poling, to fabricate fine-pitch domain structures in Rb-doped <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mi>KTiOP</c:mi><c:msub><c:mi mathvariant="normal">O</c:mi><c:mn>4</c:mn></c:msub></c:mrow></c:math> (RKTP). Here, we use micro-Raman spectroscopy to understand the impact of IE on the vibrational modes related to the Rb/K lattice sites, <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mrow><e:mi>Ti</e:mi><e:msub><e:mi mathvariant="normal">O</e:mi><e:mn>6</e:mn></e:msub></e:mrow></e:math> octahedra, and <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:mrow><g:mi mathvariant="normal">P</g:mi><g:msub><g:mi mathvariant="normal">O</g:mi><g:mn>4</g:mn></g:msub></g:mrow></g:math> tetrahedra, which all form the basis of the RKTP crystal structure. We analyze the Raman spectra of three different RKTP samples: (1) a RKTP sample that shows a poled domain grating only, (2) a RKTP sample that has an <j:math xmlns:j="http://www.w3.org/1998/Math/MathML"><j:msub><j:mi>E</j:mi><j:mi mathvariant="normal">c</j:mi></j:msub></j:math> grating only, and (3) a RKTP sample that has both an <l:math xmlns:l="http://www.w3.org/1998/Math/MathML"><l:msub><l:mi>E</l:mi><l:mi mathvariant="normal">c</l:mi></l:msub></l:math> and a domain grating of the nominally same spacing. This allows us to determine the impact of IE on the vibrational modes of RKTP. We characterize the changes in the lower Raman peaks related to the alkali-metal ions, as well as observe lattice modifications induced by the incorporation of <n:math xmlns:n="http://www.w3.org/1998/Math/MathML"><n:mrow><n:mi mathvariant="normal">R</n:mi><n:msup><n:mrow><n:mi mathvariant="normal">b</n:mi></n:mrow><n:mo>+</n:mo></n:msup></n:mrow></n:math> that extend further into the crystal bulk than the expected IE depth. Moreover, the influence of IE on the domain walls is also manifested in their Raman peak shift. We discuss our results in terms of the deformation of the <q:math xmlns:q="http://www.w3.org/1998/Math/MathML"><q:mrow><q:mi mathvariant="normal">P</q:mi><q:msub><q:mi mathvariant="normal">O</q:mi><q:mn>4</q:mn></q:msub></q:mrow></q:math> and <t:math xmlns:t="http://www.w3.org/1998/Math/MathML"><t:mrow><t:mi>Ti</t:mi><t:msub><t:mi mathvariant="normal">O</t:mi><t:mn>6</t:mn></t:msub></t:mrow></t:math> groups. Our results highlight the intricate impact of IE on the crystal structure and how it facilitates periodic poling, paving the way for further development of the <v:math xmlns:v="http://www.w3.org/1998/Math/MathML"><v:msub><v:mi>E</v:mi><v:mi mathvariant="normal">c</v:mi></v:msub></v:math>-engineering technique. Published by the American Physical Society 2024